Located in Belgium, the Caves of Remouchamps has among its many wonders the longest subterranean river known in the world. Opened in 1912 and originally equipped with torches, the caves are explored in two parts. The first is a long walk to a grand "cathedral", followed by an hour and a half boat ride down the caves' quiet and entirely underground river, the Rubicon. Floating down the underground river gives the impression of an entering a lost underground fairy kingdom.

The history of the Caves of Remouchamps is also quite unique. Some 8,000 years ago, Paleolithic hunters sheltered themselves in the cave, and much later, the same area was used as a wine shelter, and a shelter during World War II.

Throughout the cave there are a handful of remarkable sites for visitors to see. Bat sightings are a treat for guests and while drifting on the Rubicon, look closely for the niphargus, a blind, translucent shrimp. Many stalactites and stalagmites decorate the interior of the passageways, one famously noted for its resemblance to the Virgin Mary.