Gassan-Toda Castle has a history of transformation from a medieval castle to a modern castle, and its unique feature is the layout that skillfully uses the terrain of the entire mountain. From the foot of the mountain to the summit, multiple enclosures and moats are arranged in stages, and many ingenious measures are put into preventing enemy invasions. In particular, the steep slope called "Nanamagari" leading to the main enclosure, Honmaru, Ninomaru, and Sannomaru, which are the main enclosures, recalls the fierceness of the attacks and defenses at that time. There are many things to see, such as Taikodan, where a bronze statue of Yamanaka Shikanosuke stands, and Senjodaira, which has a vast space.

This castle reached its peak during the time of Amago Tsunehisa, and spread its influence throughout the Chugoku region. However, it was captured by the Mori clan in 1566 (Eiroku 9), and the Amago clan's influence has greatly declined since then. After that, it came under the control of the Mori clan, and after the Battle of Sekigahara, the Horio clan served as the castle lord, and the castle was developed into a modern castle. In 1611 (Keicho 16), the Horio clan built a new castle in Matsue, and the castle was abandoned.

The Gassan Toda Castle ruins are now maintained as a hiking trail, and it takes about an hour to walk from the Yasugi City Historical Museum at the foot of the mountain to the summit. Along the way, there are information boards explaining the castle ruins, so you can stroll while thinking about the history of the Sengoku period. The view from the summit is wonderful, with a panoramic view of the former castle town and the Iinashi River, and if the weather is good, you can even see the Sea of ​​Japan in the distance.