The remains of the Castle can be visited
Obermaggenberg Castle (Ruin) (Alterswil)

Above Alterswil in the canton of Fribourg, Switzerland, stands the ruin of Obermaggenberg, once a hilltop castle.
History+
The family of Maggenberg, who named themselves after their ancestral castle Niedermaggenberg since the founding of Fribourg in 1157, initially served the Zähringer and later the Counts of Kyburg and the Habsburgs. Between 1250 and 1350, they provided the mayor of Fribourg seven times. Ulrich II von Maggenberg, a close confidant of Rudolf von Habsburg, is presumed to be the builder of Obermaggenberg Castle in the 12th century.
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: 46.7834, 7.3010