A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

The world's longest and deepest train tunnel.

Featuring one of the most complete and original collections of Presidential memorabilia, this is the site of the last front porch presidential campaigns.

This large midwestern cavern features impressive rock formations and an underground waterfall.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Software company Epic Systems has created one of the strangest and largest workplaces of all time.

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

Amidst the bustling streets of Dublin, there is a hushed garden that is dedicated to "All those who gave their lives in the cause of Irish Freedom."

A particularly disconcerting tribute to Irish martyrs.

One of Ireland's most infamous prisons for rebels including men, women and children.

This grave marks the passing of a historic Jane Doe whose identity remains a mystery to this day.

Rusting ships sit in a desert where a sea used to be.

Blighted Irish field and the ruins of a 19th-century cottage on the edge of urban Manhattan.

Mysteriously stacked storefront paths give this medieval British town an iconic style like none other.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

This "preacher's pulpit" once used for pagan ritual, is home to a new, and dangerous ritual.

The world of the ancient Celtic civilization explained through a bewitching 11 acre garden.

A dilapidated dock tells the story of Titanic's missed arrival.

An Irish church where an 800-year-old mummy is reaching out of his coffin as if to shake hands.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

The ancient tomb acts as a calendar that keeps perfect time.

A walk through the historic city center, under the streets of Seattle.

In this relatively flat state the highest point is an honored place.