Tác, the nearest village van be reached easily from M7, the motorway between Budapest and Lake Balaton. Gorsium is the ancient roman name of the place, afterwards called Herculia.
In Hungary, we have a local national website for geocaches, http://geocaching.hu - caches can only be logged with a password found in the cache. In the case of a virtual cache this should be a inscription or something else that can only be get known at the given coordinates. The password of this cache can be read on a tombstone, the name of the person.
Important: this museum is open 8-18 (april-october) and 8-16 (november-march), any other times you can't reach the cache. Entry fee: 250 HUF (about 1 USD).