Burg Allerburg, Medieval castle ruins in Sonnenstein, Germany.

Burg Allerburg, also called Ellerburg, is the ruin of a hilltop castle on the isolated 323 m Allerberg near Bockelnhagen. Its small summit, about 25 by 35 m, held an upper and a lower bailey surrounded by a ditch. The 19th-century brick and half-timbered replacement built by Baron August von Minnigerode is now also ruined.

The castle was probably built before the 12th century by the lords of Allerberg, ancestors of the von Minnigerode family. It was first documented in 1266 as the seat of the Minningerode family, linked to the county of Lutterberg-Scharzfeld. In the 14th century the counts of Hohnstein and later the landgraves of Hesse held rights to it, and it was enlarged before passing partly to the counts of Schwarzburg. In 1525 rebellious peasants destroyed it during the German Peasants' War.

The name Allerburg alternates with Ellerburg, after the Weilroder Eller stream in the valley below. In 1408 a chaplain named Heinrich Blicherod was recorded at Allerberg, witnessing the appointment of a parish priest in the nearby village. The castle held a defined district: Bockelnhagen, Silkerode, Zwinge and the Neue Hof, plus the deserted villages of Ankerode, Kirchdorf, Möncherode, Hochstedt, Besselhagen and Weilrode.

The summit is reached on foot via forest paths; an old sunken track (Hohlweg) still leads from the valley up to the hilltop. The small plateau measures only about 25 by 35 metres, so the circuit is short. Below the summit there is a shelter hut and several information boards.

The present ruin on the summit is not medieval: before 1930, Baron August von Minnigerode replaced the last remains of the old castle with a new brick building topped by half-timbering. That structure has since fallen into ruin as well, so the fragments visible today are largely the remains of this early 20th-century reconstruction.