I have found two underground caches:
Kalte Kuchl, Austria - cave under huge blocks of rock.
#2 Alvarez, Czech Republic - mystery cache, seeking for indicies in cave full of dry sand...
I want to found this caches sometimes...
Styx
Reisenturmhöhle
Some central Europe:
Ralsko castle, Czech Republic (GCX3DZ)
GCW7NT, Czech Republic
GCNPPK, Czech Republic
GCMEFF, Austria
GCW8A1, Austria. 2hr hike with 600m height gain ... and DNF