Harmanecká Cave or Harmanec Cave (Slovak: Harmanecká jaskyňa, Hungarian: Hermándi barlang) is a stalactite cave in Central Slovakia. It is located on the northern side of the Kotolnica massif in the Staré Hory and Kremnica mountain ranges and south of the Veľká Fatra mountains. The closest villages are Harmanec and Dolný Harmanec; Banská Bystrica is around 16 km south east of the cave. It is formed from Middle Triassic dark-grey Gutenstein limestone with an estimated age of 220 million years. The entrance to the cave is situated at an altitude of 821 m and 260 m above the bottom of the Harmanec valley.
The entrance to the cave had long been known to local people. They used it as a shelter during bad weather and called it Izbica. But it was only on 22 June 1932 that the 18-year-old Michal Bacúrik discovered the cave. While he was doing a detailed survey of the entrance, he found a narrow fissure to the cave itself. Through this fissure he noticed a strong draft and bats were flying in and out. This made him assume that the cave spaces were located behind this fissure. At this spot the entrance door of today´s cave is located. After two weeks of digging he was able to enter the first parts of the cave. Soon the speleologists discovered other parts of the cave. The cave was opened to the public in 1950 en in 1972 it was registered as a national monument.
Up to now, more than 2,700 m of underground passages have been discovered but only 720 m are open to the public. The air temperature varies between 5.8 and 6.4° Celsius. The humidity is between 92 and 94 percent.
The Explorer´s Dome is the first dome that is reached by visitors through the artificial passage from the entrance. The dome holds many different forms of sinter decoration like stalactites, stalagmites and sinter columns. The sinter decoration is made from atmospheric water filtering through the cave roof and by precipitation of calcite from water. A one cubic millimeter of dripstone decoration in this cave takes approximately 10 to 15 years to grow.
The White Gothis Dome is named after the shape of the ceiling which resembles a Gothic vault and also after the characteristic white colour. Because the cave roof is formed from chemically clean chite calcite, the decoration has a pure white colour. This white colouring is very specific for the Harmanec cave. If the roof contained different elements of metals it would be more colourful. A sinter waterfall called the Tongue of the mother-in-law can be seen hanging from the ceiling. These parts of the cave, till the end of the white gothic dome were discovered by Michal Bacurik. The other parts were discovered in 1938 by Ondroušek and Kovalčik.