Burgruine Dreienburg, castle ruin

Burgruine Dreienburg, also known as Alter Keller, is a ruined spur castle on a promontory at about 441 m on the southeast side of the Dreienberg in the Kuppenrhön. Visible are the foundations of a square residential tower 8.5 m per side, partly built of bossed ashlar, a neck ditch on the mountain side, and an outer rampart and ditch. A depression at the east end marks another building and the original access from the southeast.

The castle likely arose during the 1200s as a fortification built by Hersfeld Abbey and first appeared in written records in 1257 when Hartwig de Dringenberg was noted as its owner. The structure began to decay after the late 1500s and was marked on maps as a ruin by 1592.

Locals call the ruin "Alter Keller" (Old Cellar). The name Dreienburg is recorded from 1257, when a lord was styled Hertwig von Drigenberg; a 1428 border description mentions a watchpost at Lautenhausen that may be the same site. The ruin was last mentioned in 1642.

The site is freely accessible at any time and reached on foot through a short walk in the woods from a parking area. There are no facilities at the location, so bring water and plan your visit during daylight hours.

Locals call the ruin "Alter Keller" (Old Cellar), a nickname not explained in the records. The square residential tower had sides of 8.5 m, and parts of its foundation walls are built of bossed ashlar blocks. Wall remains were uncovered in 1901 and again during unauthorised digging in 1973.