Movile Cave, a few kilometres from Mangalia, is one of the most remarkable biological sites on earth, though it is not accessible to ordinary visitors. The cave was sealed approximately 5 million years ago, and the ecosystem within has evolved in complete isolation ever since — no light, no organic matter from outside, sustained entirely by chemosynthetic bacteria that process hydrogen sulphide from the underground water.
The 48 species so far identified include spiders, scorpions, isopods, leeches, and other invertebrates, all adapted to the permanent darkness, toxic atmosphere, and complete absence of the photosynthetic food chains that underpin virtually all other life on earth. Access is strictly controlled by Romanian authorities and limited to a handful of scientists per year. The cave's existence is a reminder that Mangalia sits on a geologically unusual terrain, with warm sulphurous springs that feed both the cave chemistry and the spa treatments for which the town is known.