The approximately 22 m long Gudenus cave is located in the west of the city of Krems about 8 m above a riverbed below the castle Hartenstein. It is probably one of the oldest settlements in Central Europe. In 1884, some local historians under the guidance of the Benedictine priest Leopold Hacker from Göttweig (at that time pastor of Purk) examined the cave. It was extremely tedious since the entrance was only 90 cm high. The cave is named after the Gudenus noble family resident today in Albrechtsberg on the Great Krems.
Finds come from the lower cultural layer (about 70.000 years ago) as well as from the upper cultural layer (between 20.000 and 10.000 BC). Neanderthals hunted mammoths, woolly rhinoceros, reindeers, wild horses, and cave bears in the area. The most important finds are a 4 cm long bone pipe which is the oldest musical instrument in Austria. There is also the incised drawing of a reindeer head on an eagle bone. You can see both in the Natural History Museum in Vienna.
The starting point for the hike to the Gudenus cave near the Hartenstein Castle is the Maigenmühle on the road from Weinzierl am Walde to Albrechtsberg. The path leads along a forest road along the Kleine Krems to the castle and takes about one hour.
A geological trail in the immediate vicinity provides insight into the formation of the mountain and the geological structure of the area in nine stations. It also provides explanations of typical rocks.
More info on Wikipedia.