Are in fact galleries of a former quartz sand quarry. By construction, this is a system of parallel and crossing passages with sandstone columns left to support the ceiling separating the galleries. This deposit of good quartz stone was discovered by geologist Hendrik Bekker in 1920. Mining of the light sandstone of the Gauja bed of the Sventoji stratum started here in 1922; industrial mining started in 1924 from Mõrsjamäe. At the beginning, mining was done in adits and the sand was carried out in trolleys. This kind of mining was finished in 1966, when a quarry was opened north of these caves, and by 1985, the annual production of this quarry was 28,000 tons.
The caves were closed in 2006 due to the danger that the caves would collapse. After closing the openings and stabilising the ceiling, the caves were opened for visitors in 2008 as the Piusa Cave Museum with a sightseeing platform.

In the caves of Piusa, there is a Museum Cave with a sightseeing platform opened for visitors. The sightseeing platform is opened from May 15 to September 15, every day from 11 a.m. to 7 p.m.
Hiking trail in Piusa
There is a 1.4 km trail starting from the caves of Piusa; there one can take a look at the beautiful heath forest and walk in the healthy air of the pine forest. The trail is outfitted with information stands describing the nature. The trail ends at the parking lot.
If you take this walk, we ask you to stay on the marked footpath only, because:
There are places near the footpath that are situated above the roof of the caves liable to collapse;
The lichen communities of these forests are very sensitive to trampling, especially in dry weather.

Sources

http://www.piusamaa.ee/#