Dating back almost 400 years, the oldest public collection library in the United Kingdom was once the study hall of Karl Marx.

These ancient symbols freckling a Scottish cliff remained hidden for centuries.

This observatory within Europe's first dark sky park offers stunning views of the night sky.

The ruins of an 800-year-old monastery boasts the tallest round tower in Ireland.

An Iron Age fort on the edge of a seaside cliff offers a glimpse into an ancient, mystical world.

A moody and picturesque riverside ruin overgrown with vegetation.

The remains of centuries of copper mining appear like an alien landscape.

These haunting ruins belong to an ancient village that once had one hell of a view.

A hidden tunnel leads to an abandoned slate quarry that's now a secret swimming spot guarded by cliffs.

The stately remains of Llywelyn the Great's mighty fortress.

The largest cave chamber in Britain—big enough to fit a whole cathedral inside.

A group of glacial erratic boulders are improbably balanced on white limestone pedestals.