Falkensteiner Höhle cave in southern Germany. Really, a high dynamic range image.
Every scene like this is very hard to be properly photographed. If the cave's interior is to be visible on the photo, the view outside is overexposed. On the other hand, getting properly exposed exterior means that no details inside are visible. The above result was achieved by combining 4 photos to HDR using "Smart-Merge" method. The tone mapping parameters were default.