The Roman Castle can be visited
Roman Castle Marköbel

The Roman Fort Marköbel was a Roman fortification on the Upper Germanic-Rhaetian Limes. It is located in Marköbel, a district of Hammersbach in the Main-Kinzig district, and served to monitor an important Limes crossing over the Krebsbach stream.
History+
The location at the crossing of a pre-Roman trade route, which later became the Hohe Straße, led to the search for a fort as early as the 19th century. Initial field surveys took place in 1881. In 1884, Georg Wolff was able to prove the existence of the fort after remains of the civilian settlement had been investigated. Under Wolff's direction, further excavations were carried out by the Imperial Limes Commission in 1892 and 1893. Large parts of the fort and its associated civilian settlement were built over in the 20th century. In 1951, during the installation of heating in the Protestant church, foundations of the bathhouse were discovered, which were partially uncovered between 1963 and 1965. The last undeveloped area in the northwest of the fort was archaeologically investigated in 1983. The stone fort, which covered 3.3 hectares and was oriented to the east, had a 1.20 to 1.30 meter wide cast wall and was surrounded by a double pointed ditch.
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: 50.2227, 8.9842