Děvín, Castle ruin in Hamr na Jezeře, Czech Republic.

Děvín is a castle ruin on the 436-metre summit of the same-named hill in the Ralská pahorkatina, within the Děvín a Ostrý nature monument. Its core had perimeter buildings, with a rectangular bastion-like projection and the lower level of a square tower in the eastern corner. A horseshoe-shaped artillery bastion and an arched portal, possibly a lift remnant, survive in the outer fortification.

The fortification was built during the Middle Ages and played an important role in controlling trade routes across the region. Its hilltop location made it useful for monitoring the surrounding area during periods of conflict.

The castle's name comes from the personal name Děva, rooted in the Old Czech word for girl. Legends tell of a secret underground passage running about six kilometres to the church in Osečná, and of a once cruel knight whose ghost frightened a cottager from that town. Karolina Světlá worked one of these tales into her story Lamač a jeho dítě.

The best conditions for a visit occur during warmer months when paths are dry and visibility remains clear. Getting there involves following marked hiking trails that can be reached from various starting points.

The architectural remains show different building phases that reveal how defensive structures changed over time. Remnants of watchtowers and fortification walls provide insight into earlier construction methods.