Located near the village of Durness, Scotland, is Smoo Cave. This impressive geological wonder was carved into limestone by the Allt Smoo, a river that runs above and pours into the cavern through a sinkhole.
This water cave includes both sea water and fresh water. While the inner chambers were formed by the Alt Smoo, the first chamber, which features a easily accessible and expansive cave mouth, was formed by sea water erosion.
The cave is fairly easy to access, and there are stairs, walkways and restrooms available for the nearly 40,000 people who visit each year. Boat rides are offered within the inner watery caverns during the summer.