This looks like the underground dwelling of the Tuatha de Danaan, or "Children of Danu", the mythological mother goddess of the Irish Celts. Creatures such as leprechauns and other Fairy Folk were known to inhabit these places, particularly under the burial mounds, which were also known as the fairy mounds for that reason.
Stone house in the forrest of Denmark The story of this house: When the german were in Denmark in worldwar 2, they took over a mans farm. This man moved into the deep forrest and made this house of stone. Around the house is a moat. This plase is in Jylland, behind Tirstrup airport.