Temple inside Phraya Nakhon cave, Thailand. Photo by: Georgi Iashvili

S?n ?oòng cave, Vietnam, as of 2009 it is the biggest known cave in the world. Photo by: Peter Carsten | National Geographic

S?n ?oòng cave was created 2-5 million years ago by river water eroding away the limestone underneath the mountain Where the limestone was weak, the ceiling collapsed creating huge skylights. Photo by: Carsten Peter

Illuminated cave pools. Photo by: unknown

Black hole of Calcutta, Australia. Photo by: Carsten Peter | National Geographic

The world’s largest underwater cave, Russia. Photo by: Viktor Lyagushkin

Castle within a cave, Predjamski Grad, Slovenia. Photo by: unknown

Blue marble cave, Chile. Photo by: Robert O’Duill

Maya`s natural well inside cave, Guatemala. Photo by: unknown

Deep blue iced cave, Iceland. Photo by: Orvar Thorgeirsson

Buddha Temple inside Datdawtaung Cave, Myanmar. Photo by: Lin Tun

Restaurant inside a cave, Italy. Photo by: Grotta Palazzese