Coordinates: 43°49′32″N 28°33′38″E / 43.825694°N 28.560556°E / 43.825694; 28.560556
Movile Cave (Romanian: Peștera Movile) is a cave near Mangalia, Constanța County, Romania discovered in 1986 by Cristian Lascu a few kilometers from the Black Sea coast. It is notable for its unique groundwater ecosystem abundant in hydrogen sulfide and carbon dioxide, but low in oxygen. Life in the cave has been separated from the outside for the past 5.5 million years and it is based completely on chemosynthesis rather than photosynthesis.
The air in the cave is very different from the outer atmosphere. The level of oxygen is only a third to half of the concentration found in open air (7–10% O2 in the cave atmosphere, compared to 21% O2 in air), and about one hundred times more carbon dioxide (2–3.5% CO2 in the cave atmosphere, versus 0.04% CO2 in air). It also contains 1–2% methane (CH4) and both the air and waters of the cave contain high concentrations of hydrogen sulfide (H2S) and ammonia (NH3).