This ruin may not look like more than a pile of red-brick rubble, but it actually preserves a piece of Denmark’s past. It’s the sole survivor of a lost 16th-century fortification.

Jarmers Tower (Jarmers Tårn) is the only remnant of the old wall that once wrapped around Copenhagen. The tower, which was part of a fortification built in 1520, was named after the Wendish prince Jaromar II of Rügen, who in 1259 successfully attacked the city near the spot where the was later built.

Originally, Jarmers Tower was one of 11 different defense towers. But as the city outgrew its wall, both the wall and most of its towers were lost to time. The sole surviving bit was restored after the area around it was excavated in the 1880s. Now, it stands preserved as a ruin within a small plaza also named after Jaromar.