Szemlö-Hegy Barlang is famous for an extraordinary amount of a rather rare speleothem called cave popcorn, or more serious cave coral. It forms popcorn, cauliflower or disk like structures, covering walls and ceiling. There are many extraordinary speleothems including helictites.

The enormous amount of those generally rare speleothems is a result of the geothermal speleogenesis of this cave. The groundwater is heated by geothermal energy, and thus both cave formation and speleothem formation is speeded up. On the other hand there are normal kartification processes going on, and the groundwater is lowered by the cutting in of the stream channel. In this case the Danube is draining the karst area, and today drainage is at the level of the river Danube.

The show cave is also the seat of the Hungarian Speleologic Society, it is used for speleotherapy and has a reception hall.