Thiemsburg, Medieval castle in Schönstedt, Germany

Thiemsburg is a forest estate and former forestry house site in the Langensalzaer Stadtwald, part of Hainich National Park, about 340 m above sea level. At its centre stands the Nationalparkzentrum with the Baumkronenpfad, next to the rebuilt Forsthaus Thiemsburg used as hotel and restaurant. West and south of the pond, the Schanzgraben earthwork remains of a former fortification are still visible.

Thiemsburg was first mentioned in 1143, when Abbot Thiemmo of Homburg Monastery acquired the forest near the Diemarsburg from Heinrich, son of Erchenbert von Wida. The site's Schanzgraben earthwork, enclosing the pond to the west and south, may have guarded the old Zimmern'sche Weg trade route through the Hainich. Before the Thirty Years' War the estate was enlarged into a representative farmstead whose tenants kept sheep on cleared land.

The name Thiemsburg recalls Abbot Thiemmo of Homburg Monastery, who acquired the forest near the Diemarsburg in 1143. Many boundary stones from 1741 still stand around the site, carved with the arms of Bad Langensalza and of the Goldacker lords of Weberstedt. A stone cross photographed in 1933 has since disappeared.

Thiemsburg lies on a forest road about 20 km northeast of Eisenach and 10 km west of Bad Langensalza, with a hiking car park of over 300 spaces and a bus stop on site. The Baumkronenpfad Hainich, opened on 26 August 2005, begins 200 metres away. Circular trails through the Hainich National Park start here.

A stone cross at Thiemsburg was photographed in 1933 but has since disappeared; only the photograph records it. In 1915 a prisoner camp was set up on the forest house grounds, though it is unknown whether prisoners were ever held there. Behind the forest house, a sawmill of the VEB Militärforstwirtschaftsbetrieb produced wood parts, and some of its facilities still stood in 2012.