Tobigasu Castle was a mountain fortress built on the summit of Mount Tobigasu, at an elevation of approximately 281 meters, in Nishibayashigi-cho, Izumo City, Shimane Prefecture. Today, the site is preserved as a designated historic site of Izumo City.
During the turbulent Sengoku period, Tobigasu Castle was an important strategic stronghold in the struggle between the Mori clan and the Amago clan. Although the original buildings no longer remain, the surviving earthworks and other remains offer a glimpse into the castle’s past.
The site is also popular with hikers. From the mountaintop, visitors can enjoy sweeping views across the Izumo Plain, Lake Shinji, the Sea of Japan, and the surrounding mountains, making Tobigasu Castle Ruins a fascinating combination of history and natural scenery.
Tobigasu Castle is traditionally believed to have been built by Shinji Hisayoshi around 1509, during the Eisho era. The castle was subsequently renovated several times as warfare intensified during the Sengoku period.
In 1562, Mori Motonari is said to have recognized the strategic importance of the site while preparing to attack the Amago clan and strengthened the castle’s defenses.
Located north of the Izumo Plain, the castle commanded views of Lake Shinji, the Sea of Japan, and the Kitayama mountain range. Its elevated position made it valuable as a military base, as well as a place for storing supplies and stationing troops.
During the Sengoku period, the Izumo region became a major battleground between the Amago and Mori clans. Tobigasu Castle served as one of the important front-line strongholds in this conflict.
In 1571, during the Mori campaign against Takase Castle, the site was reportedly used as a base by Kikkawa Motoharu. The castle also played a role when Mori Terumoto and other forces fought the Amago revival army.
These episodes illustrate the strategic importance of Tobigasu Castle in the struggle for control of Izumo.
Following the Battle of Sekigahara in 1600, the Mori clan lost a substantial portion of its territory. The Shinji clan was also transferred to another domain, and Tobigasu Castle eventually lost its military function and was abandoned.
Although none of the original castle buildings survive, the mountain has been developed as a historic park, allowing visitors to explore the remains and imagine the castle as it once stood.
Tobigasu Castle was a renkaku-style mountain castle built along the mountain ridges. Its main enclosure, or honmaru, was positioned at the center, with secondary fortified enclosures extending outward along the surrounding ridges.
The main enclosure covers approximately 450 square meters, while around ten additional enclosures were constructed along the ridges. Many of these areas were protected by earthen defensive walls known as dorui.
Other surviving features, including cut trenches and a well, provide valuable clues about how the castle was designed and defended.
One notable feature of the ruins is a Hokyoin-to stone pagoda known as Ono-zuka. It is traditionally regarded as the grave of Ono Takanari, who is said to have been assassinated within the castle in 1582.
The story reflects the complicated relationships, alliances, and power struggles that characterized the Sengoku period.
The historical record Unyo-shi also names Shinji Takayoshi and Shinji Masayoshi as lords of the castle, providing further evidence of the site’s role as a regional center of power.
A monument honoring Shinji Masayoshi, traditionally regarded as the castle’s final lord, stands near the summit.
Standing beside the monument and looking across the surrounding landscape offers a chance to reflect on the people who lived and fought here centuries ago.
The castle ruins can be reached via a maintained hiking trail from the foot of the mountain. The trail is approximately 1 kilometer long and takes around 30 to 45 minutes to walk, making it suitable for visitors who want to enjoy a relatively easy hike.
Distance markers are placed every 100 meters along the trail, allowing hikers to keep track of their progress. Benches are also provided along the route, giving visitors places to rest and enjoy the surrounding forest.
Reaching the summit rewards hikers with a spectacular panorama. Lake Shinji can be seen to the east, while the Sea of Japan and Taisha Bay stretch to the west.
On clear days, distant mountains including Mount Daisen and Mount Sanbe can also be seen. The broad Izumo Plain, with the Hii River flowing through it, spreads out below.
Depending on the timing, visitors may even see aircraft approaching Izumo Airport, adding an unexpected element to the mountain-top experience.
Mount Tobigasu offers different scenery throughout the year. Fresh green foliage in spring, deep green forests in summer, colorful leaves in autumn, and clear winter air each create a different atmosphere.
Autumn is particularly popular, when the trees along the hiking trail become covered in vivid seasonal colors. The combination of colorful foliage, mountain scenery, and historical remains makes this an especially enjoyable time to explore the site.
The castle ruins are now maintained as Tobigasu Castle Ruins Park. Information boards, a rest pavilion, and benches have been installed throughout the area.
A historical information board near the summit introduces the structure and history of the castle, allowing visitors to learn more about the site while exploring the mountain.
Tobigasu Castle Ruins is more than an archaeological site. Walking through the forest and along the old mountain defenses while learning about the battles of the Sengoku period creates a unique experience that combines history, hiking, and nature.
The surrounding area also features historic temples and beautiful natural landscapes, making the castle ruins a worthwhile stop on a sightseeing route through the Izumo region.
The trailhead for Tobigasu Castle Ruins is approximately a 30-minute walk from Kawato Station on the Ichibata Railway. A parking area with space for around 30 vehicles is also available near the trailhead, making access by car convenient.
The hike is relatively easy, but this is still a mountain trail. Visitors should wear comfortable walking shoes and suitable outdoor clothing.
After rain, parts of the trail may become slippery, so take care with your footing and allow enough time to enjoy the walk safely.
Tobigasu Castle Ruins offers a rare combination of Sengoku-period history and spectacular natural scenery. Once an important military stronghold, the site is now a peaceful destination where visitors can explore historic remains while enjoying panoramic views across Izumo.
The journey to the summit is part of the experience. As you walk along the forest trail, you can discover earthworks, enclosures, trenches, monuments, and other traces of the former castle before arriving at the panoramic viewpoint.
For travelers interested in Japanese history, hiking, and scenic landscapes, Tobigasu Castle Ruins provides an opportunity to experience a lesser-known side of Izumo. Walk through the remains of a Sengoku mountain fortress, then pause at the summit and take in the vast landscape that once made this location so strategically important.