One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

The final resting place of the world's first nuclear reactor.

Over a thousand feet beneath the Detroit streets is a subterranean metropolis few are allowed to enter.

A boulder in the Churchyard of Down Cathedral marks the legendary burial place of "The Apostle of Ireland."

The ruins of a resort and casino sit on the banks of this blue hole spring that pumps 70,000 gallons of warm, clear water every minute.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

Walk down these stairs to get an underwater view of Switzerland's Lake Zug.

A group of college students hauled a desk up a mountain more than 40 years ago. The notebooks inside have become a makeshift time capsule.

This lab's maddening silence is good for business but bad for sanity.

If there's another drive-through golf-cart bar in a bat-filled cave on top of a mountain, we don't know about it.

To get to or from this Canadian ghost town, you'll need to cross 11 single-lane bridges.

One man has carved a number of natural New Mexico caves into psychedelic sandstone temples.

This twisty section of highway in the Himalayan foothills is lined with thousands of small mirrors.

This lookout tower built in the 1930s is now an in-demand cabin with what might be the best view of the Seneca State Forest.

The first geometric self-supporting spiral stairs in Britain are a truly beautiful sight.

Mysterious meeting place for UFO hunters near Area 51.

In 1909, the steepest and most difficult piece of track on the Canadian Pacific Railway was replaced with a series of spiralling tunnels cut into the mountains.

Light still pours into the ruins of this ancient Islamic observatory.

18m long sarcophagus of a constantly growing dead prophet.

These rose marble urinals are the most luxurious loos in Liverpool.

An actor's tribute to a former mentor.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This mansion on an island off the coast of Georgia once belonged to a 108-year-old heiress.

A 15-foot-tall statue of the head of the Sopranos family greets passengers at a train station in southeastern Lithuania.