A monument celebrating the idea of reaching inaccessible places.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

An artsy hidden staircase leads to breathtaking views of San Francisco.

A huge musical instrument played by the ocean.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A mysterious plaque to the even more mysterious "Fr. Pat Noise," killed in "suspicious circumstances."

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

These engineering masterpieces are a dominant feature of the Belfast skyline.

One of the largest lenses of its kind ever created, this former ship beacon has been brought down to Earth.

It was once nicknamed "the most bombed hotel in Europe."

A giant sculpture of the legendary "Salmon of Knowledge" celebrates the return of fish to Belfast's River Lagan.

Belfast's namesake river still winds below the city center, hidden from sight.

A palatial former bank building now houses what may be the poshest art venue (and former Tesco) in Belfast.

The statue honors a beloved bird that once roamed St. George's Market.

The last Victorian market in Belfast.

A museum marks and documents the site of the Titanic's launch.

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

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

A remarkably intact castle that once was the largest in Ireland.

A moody and picturesque riverside ruin overgrown with vegetation.

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

The whiskey producer's archives includes a historical list of infractions committed by and associated penalties exacted upon employees.

Mortarless walls that stretch for miles are a lovely solution for creating grazing land in the harsh terrain of the Aran Islands.