On the Mediterranean island of Sardinia, cave tombs were cut into the rocky hills around 5,000 years ago by the Ozieri people. The nickname "house of fairies" is modern nickname; they are officially named Domus de Janas, derived from the Roman goddess Diana. The 2,000 tombs come on all sizes.
Although now mainly used by shepherds as sheep pens, the caves cut into the rock faces of the mountains were once sealed and elaborately adorned with red paint and bulls’ heads, representing male fertility and regeneration. Vague outlines of horns and spirals still remain on the walls of some of the Domus, although the reuse of the tombs for burials into Roman times and the Middles Ages has left few of the original sites undisturbed.
See more pictures, including an interior view, at Atlas Obscura. Link
(Image credit: Wikipedia member Giovanni Seu)
This has nothing to do with Diana.