https://www.burg-grimmenstein.at/

https://www.openstreetmap.org/way/352734946 Street view (very far off): https://goo.gl/maps/4GLAH1ftcydDGyKj8

Visitation details taken from a translation of the site above. During opening hours on Saturdays, Sundays and public holidays, From February 11, 2023 to December 17, 2023, the Grimmenstein Castle Museum can be visited independently (duration approx. 15-20 minutes). Advent opening days from November 4th to December 17th

Apparently it can be rented out for events as well.

Very little about the castle’s history is publicly available on the web. The best I could find is this small write-up:

The museum-castle Grimmenstein is the most famous sight of the village of the same name. The building consists of a so-called high castle on the rock and a hillside castle below. The name of the castle dates back to the 12th century, but its foundations and parts of the masonry are much older. Some sources point to a much older history of the castle, for example, part of the preserved keep is said to date back to a Roman watchtower around 2,000 years old. After years of decay, it has been undergoing extensive renovation by the Grimmenstein family since 2014.