Mount Hottanjō, Mountain summit in Numazu, Japan.

Mount Hottanjō is a 410 m mountain on the boundary between Numazu and Izunokuni, in the Shizuoka Prefecture range known as the Shizuura Mountains, facing the head of Suruga Bay. Its summit opens to the northwest, giving views of Suruga Bay and Mount Fuji about 42 km away, while the coastline below is hidden by trees; a viewpoint on the slope looks over the inner bay.

In the Nanboku-chō period, Hatakeyama Kunikiyo built Mitsu Castle on Mount Hottanjō, according to surviving records. In 1361 he and his two brothers held this castle together with Kanayama Castle in Izunokuni and Shūzenji Castle in Izu, fighting the Kamakura kubō's forces before surrendering the following year.

In hiking contexts, Mount Hottanjō is often grouped with Shiroyama and Katsuragiyama in Izunokuni as the "Izu Sanzan". The mountain is listed among the "Shizuoka no Hyakuzan" (Shizuoka's 100 Mountains) selected by the Shizuoka Hyakuzan Kenkyūkai. The trail from Mitsu is rated technical difficulty rank A (low to moderate) and physical strength level 1 (low, day-trip possible) by the Shizuoka Prefecture mountain grading committee.

Multiple trailheads provide access from both Numazu and Izunokuni sides, with parking areas near the main starting points. Visitors should wear appropriate footwear and check trail conditions before heading up, as paths vary depending on recent weather.

The summit opens to the northwest, giving a view of Suruga Bay and Mount Fuji about 42 km away; the shoreline below is hidden by trees. A viewpoint on the mountainside instead looks over the inner coast of the bay. The mountain is listed among the Shizuoka Hundred Mountains.