Belize ... This is called the ATM Tour or ATM Cave. It's amazing, you swim in with headlamps on and climb rocks and ladders to get to different levels. On each 'platform' you observe different artifacts. It's pitch dark inside with flowing water. Once in a lifetime tour, there are 25 guides that go through special training to be allowed to take tourists in the cave.
An Ice cave in Vatnajökull ice cap, southern Iceland. Vatnajökull is the largest ice cap in Europe, around 3,100 km³ constanly changing it's formation. The texture on the "floor" is snow mixed with volcanic ash from Grímsvötn, the latest erupting volcano in Iceland, erupting in may 2011.
Crystal Cave: located on the frozen lagoon of the Svínafellsjökull Glacier in Skaftafell, Iceland. It is only possible to access it when the lagoon is frozen. The centuries old ice has had almost all of the air pressed out of the ice; once air has been pressed out the ice turns into a magically blue crystal like ice.