松岡城, Medieval castle ruins in Hitachi Province, Japan.

Matsuoka Castle, also called Tatsukoyama Castle or Tazuna Castle, is a flatland-mountain castle (hirayamajiro) in present-day Takahagi, Ibaraki Prefecture. It has no keep or yagura towers; the hilltop honmaru was the core, with the ninomaru palace and retainers' houses at its foot and the sannomaru below holding offices, kitchens and more samurai residences. Surviving earthworks include earthen storehouses, earthen ramparts and moats, and the sannomaru site is now occupied by Takahagi Municipal Matsuoka Elementary School.

The castle's origins are unclear; it was likely built by the Ōtsuka clan during the Muromachi period as a mountain castle called Ryūshiyama Castle. In 1602 Tozawa Masamori, granted 40,000 koku at Matsuoka, converted it into a hirayama-style castle and renamed it Matsuoka Castle. In 1646 it passed to Nakayama Nobumasa, a senior retainer of the Mito domain; the Nakayama moved to Hitachi-Ōta in 1707, returned in 1803, and in 1868 were formally recognized as daimyō.

The castle grounds reveal traces of medieval military organization through their remaining structures and artifacts that visitors can examine directly. Walking through the site, one understands how such fortifications shaped settlement patterns and defense strategies in the region.

The site is accessible by local bus from Takahagi Station, with information available from the municipal office about visiting conditions. The grounds are navigable on foot, though visitors should plan visits during dry weather as terrain can become slippery.

Matsuoka Castle had no keep or yagura towers; sources describe it as closer in scale to a jinya, a fortified administrative residence. The honmaru sat on the hilltop, the ninomaru palace and retainers' houses at its foot, and the sannomaru held offices, kitchens and more retainers' homes.