The remains of the Castle can be visited
Geristein Castle (Ruin) (Bolligen)

The Geristein ruin, a former medieval castle, stands on a rocky ridge above Bolligen in the Canton of Bern. Its distinctive feature is a later added Savoyard round tower.
History+
The origins of Geristein Castle date back to the 11th century, when it was initially built as a wooden fortress. It was expanded with stone structures. It served as the ancestral seat of the Barons of Geristein and had the strategic task of monitoring and securing the trade route between Bern and Aargau. After the extinction of the Geristein family at the beginning of the 13th century, the castle changed hands several times. In 1298, Geristein, which at that time was owned by the Montenach family, was destroyed by Bernese troops after the Battle of Dornbühl and was not rebuilt thereafter.
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: 46.9906, 7.5238