Grotte La Merveilleuse, Underground limestone cave in Dinant, Belgium.

Grotte La Merveilleuse is an underground limestone cave system in Dinant that extends 850 meters beneath the surface. The interior features numerous white calcite formations, natural stone cascades, and mineral deposits throughout its chambers.

Workers building a local railway line in 1904 uncovered a hole that opened into a cave carved by an underground river. It was first called Grotte de Raimpaine, after the lieu-dit Rend-Peine, then renamed La Merveilleuse for its formations.

The cave's name comes from its calcite formations, which led to the original name Grotte de Raimpaine being dropped. Around Halloween, a show staged in the cave features elves and witches alongside the real bat colony that winters in the Grande salle, with actors coached by Philippe Derlet.

Guided tours are available year-round, with frequency varying between summer and winter seasons. Visitors should bring warm clothing since the temperature inside remains constantly cold throughout the year.

The cave maintains a constant temperature between 8 and 12 degrees Celsius throughout the year. These stable conditions enable specific mineral formation processes and create a steady environment for visitors.