The remains of the Castle can be visited
Kaiserpfalz (Barbarossaburg) Castle (Ruin) (Gelnhausen)

The Imperial Palace of Gelnhausen, also known as Barbarossa Castle, like the city of Gelnhausen, dates back to a foundation by Emperor Frederick I (Barbarossa). The moated castle, formerly surrounded by the Kinzig river, was founded on 12,000 oak piles.
Just ten years after the city of Gelnhausen was founded in 1180, the palace was the scene of the Imperial Diet of Gelnhausen, where Henry the Lion was tried in absentia and his lands were redistributed. Further Imperial Diets took place there in the following years.
The decline of the palace began in the 14th century, when in 1349 Emperor Charles IV pledged the castle and the city to the Count of Schwarzburg and never redeemed them. In 1431, the Count of Hanau and Palatine Count Ludwig III acquired the palace and city from Count Heinrich of Schwarzburg. During the Thirty Years' War, the city and palace were severely damaged. Imperial and Swedish troops burned down the main building of the palace.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 50.1998, 9.1954