Millions of caves can be found worldwide, many of which are home to flora and fauna that are uniquely adapted to subterranean life. Some hide magnificent rock formations, underground lakes, or gigantic crystal formations. In these places, it’s easy to feel like you have left Earth and entered another world. 

Across the ceiling and floor of the Gadime Cave in Gadime e Poshtme, Kosovo, are multicolored stalagmites and stalactites made of marble. The various shades of blue, white, and green add a vibrant nature to the cave. In the caverns of the Waitomo Glowworm Caves, the entire complex is illuminated by various species of bioluminescent larvae.

From a surreal grotto in Portugal to a cave filled with technicolored fluorescent minerals, here are 21 caves that feel absolutely otherworldly.