Cave of Crystals (Mexico): world's largest known natural crystals
Majlis al Jinn Cave (Oman): world's second largest cave cham

Waitomo Glowworm Cave (New Zealand): a glowworms' paradise

Eisriesenwelt Ice Caves (Austria): largest Ice Caves known to man

Cave of the Ghost (Venezuela): so vast that two helicopters can comfortably fly into it


