Hammershus is the largest castle ruin in Northern Europe still preserved from the Middle Ages. Hammershus is situated at the Northern part of Bornholm in an area called Hammeren, which is placed 74 meters above the ocean's surface.

Hammershus stems from the beginning of the 1200s and was built as a living accomodation for King Valdemar 2. and as a base for the crusades. Hammershus was also at some point the residence of the archbishop of Lund.

After the Reformation, Hammershus once again belonged to the King of Denmark - however, now it functioned as a state prison. Corfitz Ulfeldt and Leonora Christine, who was imprisonated in 1660, was just some of the noble prisoners held at Hammershus.  

From 1743 until 1822, Hammershus was used as a quarry, but was thereafter protected by the king.

The Hammershus fortifications with its towes fills up 35.000 sq.m. and is surrounded by cliffs.