Dom im Berg - Performance space inside Castle Rock (Schlossberg) in Graz, Austria with access via tunnel

Schlossbergtunnel (Tunnel through Castle Rock also provides
access to Dom im Berg) 

Walking through the Mountain in the Center of Town: The Schlossberg Tunnel

Entry point on the East side 

The tunnel entry on the East side is reached from Karmeliterplatz through the gate in the middle of the building facing the Schlossberg by walking up the cobble-stone street aptly named "Am Fuße des Schlossbergs" (at the foot of the Castle Rock).