Underneath Castle Hill, the rock is a maze of caves and passageways that have been used for various purposes since prehistoric times. In World War II, some were fortified as an air raid shelter and emergency hospital. 

Now known as the Hospital in the Rock Nuclear Bunker Museum (SziklakórházAtombunker Múzeum), this site was, at the time of the Cold War, further secured against nuclear contamination.

This former hospital and bunker is well worth exploring and features a variety of exhibitions on the kind of lifesaving efforts seen here during the Siege of Budapest in World War II.