Burg Seeburg, Medieval castle ruins in Hartershausen, Germany.

Burg Seeburg is a sandstone castle ruin in Hartershausen that sits along a waterway in the Vogelsbergkreis region of Hesse. The walls follow the water and form the remains of a fortification that controlled access through this area.

The castle was probably built in the 12th century to protect the possessions of Fulda Abbey. The influential Lords of Schlitz, first documented in 1116 with Ermenoldus de Slitese, are considered possible builders. The castle's destruction in the 13th century may be attributed to Bertho II. von Leibolz.

The ruin is also called Burg Hartershausen or Alte Mauer, and the name Seeburg points to the water castle it once was. It is one of seven castles in and around Schlitz, alongside Vorderburg, Hinterburg with its Hinterturm, Ottoburg, Schachtenburg, Schloss Hallenburg and the vanished Burg Niederschlitz.

The ruin stands on a hill about 1,100 metres west of Hartershausen and slightly above the village, on the slope below the Seeberg. A spring rises on the eastern slope roughly 450 metres from the former castle site, halfway to the village. The site is a listed cultural monument; walls and ditches have been levelled, so the remains are best viewed from the surrounding ground.

Of the former castle, only the eastern half of the bergfried survives, with remains of a fireplace on its inner side. The ramparts and ditches have been levelled, and the ruin stands as a landmark clearly visible above Hartershausen.