Niedaltdorfer Tropfsteinhöhle, Show cave in Niedaltdorf, Germany.

Niedaltdorfer Tropfsteinhöhle is a 120-metre primary tuff cave in Niedaltdorf, part of Rehlingen-Siersburg in the Saarland. It formed about 8,000 years ago inside a spring-limestone deposit 200 metres long, 40 metres wide and eight metres thick. Inside, a circular route links the eastern and western passages via cross-passage 2, and electric lighting was installed when the cave opened as a show cave.

Workers discovered the cave in 1880 beneath a restaurant foundation, but it was filled with construction debris. After its rediscovery in 1927, the cave opened to the public in 1932.

The cave shows how visitors once took pieces of stone as souvenirs, which led authorities to protect the site as a natural monument. Today, people can walk through and observe the formations without disturbing them.

The cave was closed for renovation in 2014 and reopened to visitors on 5 July 2026 after works costing 650,000 euros. The tour follows a circular route linking the east and west passages via cross-passage 2, with electric lighting installed when the show cave opened in 1932.

The cave is a primary tuff cave formed in a spring-limestone deposit about 200 metres long, 40 metres wide and eight metres thick, laid down over the last 10,000 years at the spring of a tributary of the Nied. The cave itself is only about 8,000 years old and 120 metres long. Look for large clear to translucent calcite crystals in the rock.