At night, bats patrol this magnificent 18th-century space in search of book-eating pests.

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

Houses are tucked between, on, and underneath giant boulders.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

The verdant mossy ruins of a Franciscan monastery lie in the remote Sintra hills awaiting exploration.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

In Portugal, a secluded stretch of untouched natural beauty hides at the bottom of a steep hill.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

This otherwise ordinary close on the Royal Mile constituted the end of the world for Edinburgh’s poorest residents.

Atop this media building, two hives containing more than 30,000 bees keep the surrounding area vibrant.

Art deco landmark on the outskirts of Washington, D.C.

The United States Capitol's former columns still stand.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

Detailed facade of a brownstone in Boerum Hill.

This innocent-looking townhome is actually a subway exit.

A clock set into the concrete outside a Manhattan jeweler has been telling time underfoot for over a century.

A quiet and contemplative oasis in the middle of New York's bustle and riot.

Monty Python fans will recognize this abandoned mine as the Cave of the Killer Rabbit of Caerbannog.

This seaside Italian village doesn't just look Escher-esque, it actually inspired the mind-bending artist.

Deceased nuns were placed on stone chairs to decompose, while the surviving nuns prayed near the lifeless bodies.

More gold than anywhere else, ever.

This scenic fortress dates back at least 2,400 years to the time of Magna Graecia.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.