An 1814 castle that hosts an exhibit of "explorabilia".

The largest portal tomb in Europe has a capstone weighing around 150 tons.

Oliver Cromwell once seized the land under this house, which included the ruins of a medieval abbey that the owner used to build his stately home.

Behemoth, cannon-like telescope operated by generations of Irish earls.

Achill's most recently abandoned village dates back to to the Age of Enlightenment.

An important pilgrimage site for pagans and early Christians, named for a Celtic goddess-turned-saint.

Just another ancient, mysterious Irish stone circle.

Wander among the abandoned ruins of this once-powerful medieval town.

This single room has survived the centuries with almost no deterioration.

The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

There might not be much left of these Irish ruins, but their linguistic legacy is still going strong.

While only two of the ancient buildings at this site are actually churches this was one of the earliest Irish pilgrimage sites ever.

This Irish show cave is said to have been the site of a Viking massacre that claimed 1,000 lives.

Once the longest bridge in Ireland, this rusting span sits abandoned and overrun by nature.