Altsachsenheim, Medieval castle ruin in Sachsenheim, Germany.

Altsachsenheim is the ruin of a hilltop castle on the edge of the plateau above Untermberg in the Enz Valley, at 230 m above sea level. Its core is almost square, 30 m north to south and just under 28 m east to west, with walls up to 14 m high and about 3 m thick, 2.4 m on the valley side. Corbels inside show the former buildings had three storeys.

The stronghold was built in the second half of the 1200s and served as the main seat of the Sachsenheim lords for generations. It changed hands to the Nippenburg family in the early 1400s and gradually lost its former importance.

The site once symbolized authority over the valley and the trade routes passing through it. People recognized the stronghold from a distance and understood who controlled this territory.

The ruin stands at the edge of the plateau above Untermberg in the Enz valley, at 230 m above sea level. A steep sunken lane (Hohlweg) leads west of the castle down from the Egartenhof hamlet to Untermberg. The south wall of the core castle runs barely one metre behind the boundary between Großsachsenheim and Untermberg.

The inner walls still carry corbels that show the former buildings rose to three storeys, not four. The south wall stands barely one metre from the boundary between Großsachsenheim and Untermberg, suggesting Untermberg vintners later bought plots after the castle was abandoned.