The Piusa sand caves in south-eastern Estonia are man made. In 1997 we found them in the wall of a quarry. The entrances were a little bit hidden. You could walk quite a bit into the cave, or rather, mine. It seemed in disuse, and was probably not at all safe to enter! In 2003 an official entrance was open a little further in a side road.
There are two parts to the sand mining activity in Piusa, the caves there were created by miners in older times and the open air quarries made more recently. Both are now in disuse.
The following are some pictures from inside the sand caves taken in 2011, replacing a photo from 2003.
Copyright Otto de Voogd 1997 & 2011