Plesse Castle, Medieval castle in Bovenden, Germany

Plesse Castle is a ruined hilltop castle on a 350-metre spur of the Wittenberg above Eddigehausen, near Bovenden. Its main tower, the Bergfried, is a cylindrical structure of light Muschelkalk limestone with walls 4.24 metres thick and a diameter of 15.26 metres; it was reduced from 30 to 23 metres in 1542. A smaller 22-metre tower, the Sydekum, stands nearby, and a long curved retaining wall supports the raised platform.

The castle was founded around 1015 when Bishop Meinwerk of Paderborn transferred the estate to Paderborn. Over the centuries, it served as a stronghold and administrative center in the region.

The castle gave its name to the lords of Plesse, who held it from 1150 until the line died out with Dietrich IV in 1571. The former dominion's villages still belong to the Evangelical Reformed Church rather than the Lutheran state church of Hanover, a legacy of Hesse's rule and of Moritz of Hesse-Kassel's 1614 conversion of the area.

The ruin stands on a roughly 350-metre-high spur in the northwestern part of the Göttingen Forest, above Eddigehausen. It lies on the Solling-Harz-Querweg long-distance trail. The keep can be climbed by an internal staircase and gives a view over Eddigehausen and the Leine valley. The site is owned by the state of Lower Saxony and has been a listed monument since 1978.

The castle's well is documented in written sources from the 16th century, which report a shaft about 150 to 170 metres deep, worked with bucket, chain and treadwheel. Visitors in the 19th century threw stones in to test its depth, gradually filling it; after the restorations of 1853 to 1862 it is no longer mentioned. No well has yet been proven archaeologically on the site.