Glowworms, glowworms, as far as the eye can see. Okay, not literally, but the Waitomo Cave system on New Zealand’s North Island is famous for the fluorescent fauna that light up the walls, giving it the not-particularly-creative but completely acceptable ‘Glowworm Caves’ nickname. They are more accessible than most caves on this list, with rafting and adventure tours available to those looking for something a little more adrenaline-heavy.