Iwadono Castle (Otsuki City, Yamanashi Prefecture) Complete Guide: The History and Highlights of an Impregnable Mountain Castle
What is Iwadono Castle?
Iwadono Castle is a Sengoku period mountain castle located in Nigioka-cho, Otsuki City, Yamanashi Prefecture. Built on the summit of Mt. Iwadono (634 meters above sea level), this castle was known as the residence of the Oyamada clan, a local lord of Tsuru District in Kai Province, and boasted exceptional strength among castles in eastern Japan. Utilizing the steep, rocky mountain as a natural fortress, it was a crucial base for the Takeda clan’s eastern defense.
Currently, it is protected as a Yamanashi Prefecture designated historical site (designated name: Iwadono Castle Ruins) and is a popular hiking spot accessible on foot from Otsuki Station. From the summit, you can enjoy a panoramic view of Otsuki city, and on clear days, you can see the majestic Mt. Fuji.
Basic Information on Iwadono Castle
Detailed Data
- Location: Nishiyama, Tsuyose, Nigioka-cho, Otsuki City, Yamanashi Prefecture
- Elevation: 634 meters (same height as Tokyo Skytree)
- Former Province: Tsuru District, Kai Province
- Castle Classification: Mountain Castle
- Builder: Oyamada Clan
- Construction Period: Believed to be during the Tenbun era (1532-1555)
- Main Lord: Oyamada Nobushige
- Year of Abandonment: Tensho 10 (1582)
- Remains: Enclosures, moats, earthworks, stone walls
- Designated Cultural Property: Yamanashi Prefecture Designated Historic Site
- Common Name/Alternate Name: Iwadonoyama Castle
Access Information
Access by Train
- Approximately 40 minutes on foot from Otsuki Station on the JR Chuo Main Line to the trailhead (Hatakura Trailhead)
- Walking time from Otsuki Station to the summit: approximately 1 hour 30 minutes to 2 hours
Access by car
- Approximately 10 minutes from Otsuki IC on the Chuo Expressway
- Parking available at Iwadono-yama Fureai no Yakata (free)
Hiking time
- From trailhead to summit: approximately 50 minutes to 1 hour
- Descent time: approximately 40 minutes to 50 minutes
- Total time: approximately 2 hours to 2 hours 30 minutes round trip
Topography and characteristics of Iwadono-yama
Iwadono-yama, as its name suggests, is a mountain with a steep, rugged appearance featuring massive exposed rocks. Its elevation of 634 meters is coincidentally the same height as the Tokyo Skytree, and it is affectionately called “Iwadono Skytree” by locals.
The entire mountain is composed of tuffaceous bedrock, and its topography, with its series of nearly vertical cliffs, truly functioned as a natural fortress. This steep terrain is the primary reason why Iwadono Castle was considered “impregnable.” It was extremely difficult for enemy forces to climb these rugged mountains, allowing even a small number of defenders to withstand a large army.
The south and east sides of the mountain are particularly steep, with only a few hiking trails on the north and west sides. This terrain was utilized to its fullest potential in the construction of the castle during the Sengoku period.
History and Development of Iwadono Castle
Heian to Kamakura Periods
The history of Mount Iwadono is ancient; it is said that Entsuji Temple, a Tendai Buddhist temple, was founded near the summit around the end of the 9th century. During the medieval period, it flourished as a training ground for Shugendo practitioners and was considered an important place of mountain worship. This religious background is thought to have formed the basis for the later construction of the castle.
Sengoku Period: The Oyamada Clan’s Castle
Iwadono Castle is believed to have been fully developed as a mountain castle during the Tenbun era (1532-1555) of the Sengoku period. The Oyamada clan, who ruled Tsuru District in Kai Province, established their castle here.
The Oyamada clan was one of the important retainers of the Takeda family, and Oyamada Nobushige, in particular, was a renowned general counted among the Twenty-Four Generals of the Takeda. The Oyamada clan ruled this area for generations, controlling the Tsuru District from Iwadono Castle.
Relationship with the Takeda Clan
During the time of Takeda Shingen, Iwadono Castle played a crucial role as a key point in the eastern defense of Kai Province. As a military base against the neighboring Hojo and Imagawa clans, and even the Uesugi clan of Echigo, it was an indispensable fortress for the Takeda family.
Its fortifications were highly regarded within the Takeda family, and Shingen himself is said to have recognized the strategic value of Iwadono Castle. The castle’s defensive capabilities, utilizing its steep, rocky terrain, were unparalleled in eastern Japan at the time.
Takeda Katsuyori and Iwadono Castle
In 1582, the Takeda clan faced extinction due to the invasion of the Oda-Tokugawa allied forces. It is said that Takeda Katsuyori planned to escape to Iwadono Castle as his last stronghold.
Katsuyori requested entry into Iwadono Castle from Oyamada Nobushige, but Nobushige ultimately betrayed Katsuyori and refused entry. This betrayal led to Katsuyori’s suicide at Mount Tenmoku, and the Takeda clan’s downfall. However, Oda Nobunaga also did not forgive Oyamada Nobushige’s betrayal, and Nobushige was executed.
This tragic event has made Iwadono Castle a historical stage for the downfall of the Takeda clan.
From the Edo Period Onward
After the fall of the Takeda clan, Iwadono Castle came under the control of Tokugawa Ieyasu and was subsequently abandoned. While it lost its function as a castle during the Edo period, Mount Iwadono continued to be cherished as a sacred mountain and a regional symbol.
From the Meiji era onward, its value as a historical site was recognized, and it is now protected as a designated historical site of Yamanashi Prefecture.
Layout and Structure of Iwadono Castle
Main Enclosure (Honmaru)
Located at the highest point of Mount Iwadono, the main enclosure is the central part of the castle. From here, a 360-degree panoramic view unfolds, offering views of not only the city of Otsuki but also Mount Fuji and the Southern Alps. Remains of building foundations and flat areas remain within the main enclosure, suggesting the former residence of the castle lord and a watchtower.
The main enclosure is relatively small, due to the topographical constraints of the mountaintop. However, even this limited space was sufficient to fulfill important defensive and command functions.
Enclosures
Around the main enclosure, several enclosures (kuruwa) are arranged in a stepped pattern. These enclosures were used as garrisons for soldiers and storage areas for supplies. The enclosures of Iwadono Castle are cleverly positioned to utilize the steep terrain, making communication between them difficult. Even if the enemy captured one enclosure, advancing to the next was not easy.
Moats and Earthworks
Moats, built to cut across the mountain ridges, are important defensive structures to prevent enemy intrusion. Several moats have been identified at Iwadono Castle, and are particularly prominent along the northern ridge.
Earthworks have also been built in various places, surrounding the enclosures. These earthworks served to protect soldiers from enemy arrows and firearms.
Stone Masonry
Some stone masonry remains have also been confirmed at Iwadono Castle. These are traces of stonework made from processed natural bedrock and artificially constructed stone walls. The use of relatively rare stonework techniques for a mountain castle from the Sengoku period demonstrates the high level of castle-building skill of the Oyamada clan.
Ascent Route
The ascent routes to the castle were mainly located on the north and west sides. These routes were intentionally designed to be complex, preventing easy attacks by the enemy. It is believed that the current hiking trails utilize parts of these old routes.
Highlights of Iwadono Castle
Chigo-otoshi (Child’s Drop)
Located on the west side of Mount Iwadono, “Chigo-otoshi” is a sheer cliff face. This cliff, approximately 200 meters high, symbolizes the defensive strength of Iwadono Castle and overwhelms visitors.
There are several theories about the origin of the name “Chigo-otoshi,” but one theory suggests it derives from the time when it was a training ground for Shugendo practitioners, and that ascetic monks (chigo) practiced asceticism on this cliff. Furthermore, a legend remains that during the Sengoku period, enemy soldiers were pushed off this cliff.
Currently, from the Chigo-otoshi observation deck, you can enjoy a spectacular view of Otsuki city and Mount Fuji. On clear days, you can also see the Southern Alps and the Yatsugatake mountain range, making it a popular spot for breathtaking scenery.
Chain Sections
The climbing route to Iwadono Castle includes several sections with chains. These chain sections were installed to safely traverse steep, rocky terrain and are known as difficult parts of the climb.
In particular, the chain sections near the summit require climbing nearly vertical rock faces, demanding a certain level of physical strength and concentration. However, these chain sections are also where you can experience the impregnability of the castle in its heyday. You can truly understand how difficult it must have been for enemy soldiers to climb such steep, rocky terrain while armed.
Nogi Maresuke’s Poetry Monument
On Mount Iwadono, there is a stone monument inscribed with a poem by Nogi Maresuke, a military officer of the Meiji era. Nogi Maresuke is known as a renowned general who distinguished himself in the Russo-Japanese War and is also famous for committing suicide upon the death of Emperor Meiji.
In his youth, Nogi Maresuke visited Mount Iwadono and was so impressed by its magnificent scenery and history that he composed this poem. This monument is one of the important historical sites that demonstrates the historical and cultural value of Mount Iwadono.
The monument is located along the hiking trail, and many hikers stop to admire it. Nogi Maresuke’s poem is a valuable cultural asset that conveys the samurai spirit and historical weight of Mount Iwadono to the present day.
Entsuji Temple Ruins
Near the summit are the ruins of Entsuji Temple, a former Tendai Buddhist temple. While no buildings remain today, the flat ground and foundation stones confirm the temple’s former existence. Entsuji Temple is an ancient temple that existed even before Iwadono Mountain was used as a castle, and it was a center of mountain worship. It is believed that when the castle was built during the Sengoku period, this religious site was respected and incorporated as part of the castle.
Views
The view from the Iwadono Castle ruins is one of the greatest attractions of visiting this place. From the summit, the city of Otsuki spreads out below, and you can see the flow of the Katsura River and the Chuo Expressway.
On clear days, the majestic figure of Mount Fuji can be seen to the west, and its beauty captivates visitors. You can also enjoy a 360-degree panoramic view of the Southern Alps, the Yatsugatake mountain range, and the Okuchichibu mountains.
The scenery is especially spectacular in the early morning and at dusk; the sight of Mount Fuji illuminated by the rising or setting sun is truly breathtaking. Iwadono Castle ruins are also a popular photography spot for photography enthusiasts.
Hiking Routes and Precautions
Hatakura Trailhead Route
The most common hiking route is the course from the Hatakura trailhead to the summit. It takes about 40 minutes on foot from Otsuki Station to reach the trailhead, and from there to the summit is about 50 minutes to 1 hour.
This route is relatively well-maintained and suitable for beginners. However, there are sections with chains and steep rocky areas, so appropriate equipment and caution are necessary.
Fureai-no-Yakata Route
There is also a route starting from the Iwadono-yama Fureai-no-Yakata (Community Center). This route is accessible by car, making it recommended for those who want to save time. The Fureai-no-Yakata has a parking lot and restrooms, making it convenient for preparing for the hike.
Precautions During Hiking
- Appropriate Equipment: Prepare hiking boots, gloves, drinking water, and snacks. Gloves are essential due to the presence of chains.
- Weather Check: Rocky areas become slippery and dangerous in rainy weather. Check the weather before hiking.
- Time Allocation: Allow ample time to descend before sunset.
- Physical Fitness Assessment: You will need to climb approximately 400 meters in elevation, requiring a certain level of physical fitness. Plan your trip realistically, considering your own fitness level.
- Passing the Chain Section: Use the three-point contact technique and proceed cautiously on the chain sections.
- Precautions for Solo Climbing: While climbing with others is preferable if possible, inform family or friends of your destination if you are climbing alone.
Tourist Attractions Around Iwadono Castle
Otsuki City Local History Museum
This museum allows you to learn about the history and culture of Otsuki City. It also features exhibits on Iwadono Castle, providing a deeper understanding of the castle’s history. Located within walking distance of Otsuki Station, it’s recommended to visit before or after your climb.
Saruhashi Bridge
Saruhashi Bridge, one of Japan’s three most unusual bridges, is located about a 10-minute drive from Iwadono Castle. This bridge, spanning the Katsura River gorge, is known for its unique structure that doesn’t use bridge piers and is designated a national scenic spot.
Katsura River
The Katsura River, flowing through Otsuki City, is known for its clear waters and offers activities such as fishing and canoeing. A promenade is also maintained along the river, making it ideal for a stroll.
Around Otsuki Station
The area around JR Otsuki Station is home to many restaurants and souvenir shops. It’s convenient for meals after hiking or for purchasing local Yamanashi products.
Best Season to Visit Iwadono Castle
Spring (March-May)
Spring is the perfect season for hiking, with beautiful fresh greenery and pleasant weather. You can also enjoy cherry blossoms at the foot of the mountain during the cherry blossom season. However, be aware that the hiking trails can be muddy during the snowmelt period.
Summer (June-August)
Summer offers lush greenery and a refreshing breeze for hiking. However, temperatures rise, so adequate hydration is necessary to prevent heatstroke. Also, be aware of thunderstorms, and it’s important to decide to cancel your climb if the weather looks questionable.
Autumn (September-November)
Autumn is the most popular season to visit Iwadono Castle, with its beautiful autumn foliage. From late October to early November, the entire mountain is dyed red and yellow, offering spectacular views. The temperature is also comfortable, making it the perfect time for climbing.
Winter (December-February)
Winter offers the clearest air and the most beautiful views of Mt. Fuji and the Southern Alps. However, snow and ice can make the trails dangerous, so winter mountain equipment and experience are necessary. Beginners should probably avoid this season.
Cultural Value of Iwadono Castle
Iwadono Castle is not merely the site of a Sengoku period mountain castle, but occupies an important position in the history of Japanese castles. The reasons are as follows:
Value as a Natural Fortress
Iwadono Castle is a classic example of a mountain castle that makes maximum use of its steep, rocky terrain. The fact that it achieved high defensive capabilities using only natural terrain while minimizing artificial defensive structures demonstrates the wisdom of Japanese castle-building techniques.
Connection to the History of the Takeda Clan
Iwadono Castle has deep connections to Takeda Shingen and Takeda Katsuyori, famous generals of the Sengoku period. It holds particular historical significance as the stage for the downfall of the Takeda clan.
Regional Identity
For Otsuki City, Mount Iwadono and Iwadono Castle are regional symbols and an integral part of the citizens’ identity. The coincidence of its elevation of 634 meters, the same height as the Tokyo Skytree, is also a source of local pride.
Fusion with Mountain Worship
Mount Iwadono has long been an object of mountain worship and a training ground for Shugendo practitioners. The fusion of this religious background and the military function of the castle is a prime example of the characteristics of Japanese mountain castles.
Preservation and Utilization of Iwadono Castle
Currently, the Iwadono Castle ruins are protected as a Yamanashi Prefecture designated historical site, and the Otsuki City Board of Education is leading preservation activities. The hiking trails are well-maintained, and signposts are installed to ensure visitors can safely learn about history.
In recent years, “castle touring” has become a popular trend among castle enthusiasts and history buffs, and Iwadono Castle is one of the popular spots. Locally, efforts are underway to utilize this historical heritage as a tourist resource and connect it to regional development.
Furthermore, Iwadono Mountain, with its moderate difficulty and magnificent views, is recognized as an attractive mountain for hiking enthusiasts, and many hikers visit on weekends.
Summary
Iwadono Castle is a Sengoku period mountain castle located in Otsuki City, Yamanashi Prefecture, built on Iwadono Mountain at an altitude of 634 meters. It was an impregnable fortress that played an important role as the residence of the Oyamada clan and as a key point in the eastern defenses of the Takeda clan.
Iwadono Castle has many attractions, including its defensive capabilities utilizing the natural terrain of a steep, rocky mountain, its connection to the historical event of the Takeda clan’s downfall, and the spectacular views of Mount Fuji and other peaks from the summit.
Its accessibility on foot from Otsuki Station, and the fact that it can be reached in about two hours round trip, are among the reasons for its popularity. With thrilling points such as chain sections and the Chigo-otoshi (Child’s Drop), it’s a valuable place where you can experience the joy of mountain climbing and learn about history simultaneously.
When visiting Yamanashi Prefecture, why not visit the Iwadono Castle Ruins and enjoy the magnificent scenery while reflecting on the history of the Sengoku period? Be sure to have appropriate equipment and preparations so you can safely enjoy both historical exploration and mountain climbing.
