The Bystrianska Cave is the most important cave of the Upper Hron River Valley. It is known by remarkable rocky features and evolution of underground spaces, occurrence of flow stone fills.
The cave was formed in the Mesozoic Middle Triassic dark grey lime stones of the Choc Nappe with chert intercalations. There are also positions of altering pale-grey dolomites. The direction of cave passages is significantly predisposed by steep tectonic faults.
The cave reaches the length of more than 3,531 m (3,862 yd) with vertical span of 99 m (108 yd). It was formed by the submersible waters of Bystrianka flowing into the karst territory from the southern slopes of the Low Tatras Mountains in several developmental stages in dependence to the valley bottom deepening. Meander riverbed in the Old Cave is the oldest part of the cave, with an entrance situated 70 m (230 ft) above the present flow of Bystrianka. At present, the submersible watercourse is flowing through the lowest and youngest parts of the New Cave, which are situated 14 m (45 ft) lower than the 160 m (175 yd) distant submersion of Bystrianka in front of the cave. The water course appears also on the bottom of the nearby Bystriansky závrt (sinkhole), which has abyss spaces more than 650 m (711 yd) long and 165 m (541 ft) deep. The springs in Valaská are 3,300 m (3,609 yd) away from submersion with elevation difference of more than 70 m (230 ft).
The main spaces of the New Cave have narrow and high fissure passages widened by corrosion and erosion of the water course. Shorter oval passages are most frequently predisposed by interbed surfaces and they connect the narrow fissure passages in some places. The upper parts of tectonic faults are widened by corrosion of percolating atmospheric waters in several places. Also larger halls and domes are present, mostly of breakdown character (Collapsed Dome, Mostárenské Halls). The Hell Abyss 56 m (61 yd) deep opens into the lower parts of the New Cave.
Flow stone fill is dominated by curtains (Chapel), which sometimes hang from the edge of flow stone crusts formed on previous and later washed out river sediments (Baldachin). Aragonite occurs in places under the Hell.
Air temperature is from 5.7 to 6.7 °C (42.3 to 44 ºF), relative humidity 92-98%. Eight bat species were determined in the cave with the most abundant Lesser Horseshoe Bat (Rhinolophus hipposideros) and Greater Mouse-Eared Bat (Myotis myotis).