The sand caves are located in the valley of the Piusa River. The river itself is known for its sandstone deposits, their height can reach 43 metres in some places. The length of the Piusa is about 93 kilometres, with most of the river - 80 kilometres - flowing through Estonia and the remaining 13 kilometres through the Pechora district of the Pskov region. In Russia, the river is called the Pizhma.
According to legend, the legendary King Setu has been sleeping in one of these Piusa caves for several hundred years. However, this of course cannot be the case, as the man-made caves were only recently created. The caves were mined and created from 1922 to 1966 as a result of sand mining for glass production.
The Piusa Caves are underground galleries with vaulted ceilings and sandstone columns. A detailed study has already revealed that there are 6 different types of caves in the Piusa reserve. The total length of all the passages is about 10 kilometres and the total area is about 46 hectares.
.Already after the cessation of sand mining, the caves became a settlement site for thousands of bats. In 1999, the area was declared a nature reserve. Today the caves are considered the largest hibernation site for bats in northern Europe. The main danger for bats is humans. Hibernating bats are very sensitive, even a conversation can wake them up and they will have to look for a new place to hibernate. Therefore, it is necessary to behave in caves according to the rules, i.e. do not make noise, do not disturb sleeping bats, especially during their hibernation period - from September to April. In addition, it is forbidden to touch them and come closer than 1 metre, as this, firstly, prevents the bats from hibernating, and secondly, can be dangerous for humans because of diseases that can be transmitted through a bite.The Piusa caves look a lot like a temple: the vaulted walls are supported by columns 6 metres high. As the Piusa Caves are of special value today both as a man-made creation and as the largest habitat for bats, they can only be visited with a guide.
