Nixhöhle, Show cave in Frankenfels, Lower Austria

Nixhöhle is a dripstone cave in the limestone cliffs of the Pielach valley, a short way upstream from Frankenfels in Lower Austria. It lies on the south-facing slope of the Klammberg near the narrowest point of the valley. Of its 1,410 metres of passages, 350 metres are shown on guided tours, with 531 steps in each direction.

The cave formed through major movements of the Earth's crust that created breaks and folds in the rock. These geological processes shaped the underground passages and chambers over time.

The name comes from the white, crumbly calc-sinter that water, carbonic acid and humic acids dissolve and redeposit in the cave; Latin calls it nihilum album, "white nothing", and locally it is Nix, also known as moonmilk or mountain milk. Guides point out natural shapes such as the Jesus head, rune-like markings and a fish head with a Madonna-like figure behind it, and tell of a farmer who mined gold and now guards visitors as a good spirit.

The cave is reached only on foot: a secured serpentine path climbs about 20 minutes from a car park on the B 39 Pielachtal road. From Frankenfels station on the Mariazellerbahn it is roughly 1.5 km to that car park. Entry is possible only on guided tours, and the route inside involves 531 steps each way, 1062 in total.

A partial cave bear skeleton found in the Pielach valley, over 20,000 years old, was brought into the cave in April 2009 and completed with further bones in 2015. Guides also point out a relief-like face in the upper section, said in local legend to be a wealthy farmer who mined gold and repented.