CIMRM 1291 - Mithraeum (undiscovered). Osterburken, Austria.
In 1861 a Mithraeum was discovered at Osterburken in Austria. An impressive tauroctony - one of the key monuments known - was found, together with two altars, plus two small lamps, pottery remains, and fragments of coloured decoration from the walls. The excavation was abandoned when a spring was disturbed and filled the excavation with water.
Cumont gives more details.1
There are some more bibliographic details in the page for the relief, CIMRM 1292.