The island of Bornholm is the easternmost island of Denmark, about 100 km east of the rest of the country. It is geologically quite different, has 1.7 Ga old crystalline rocks with gneiss, granite, numerous gangues with diabas. This is the only location in the country where such rocks are found, so the island was mined for those rocks which were then transported to the cities by ship. The most important rocks are the granites, which were used for numerous public buildings. Also, the rock forms cliffs at the sea and sea caves, so this is actually the only place in Denmark where caves are found.