The abandoned summer estate of the former Greek Royal Family.

A fairytale island floats in the middle of Italy's little-known Lake Orta.

This geothermal hot spring hides beneath a slowly growing mineral dome.

A three-tiered waterfall plummets from a mountain cave with amazing views over the countryside.

Renaissance villa and gardens complete with a tormented colossus.

The Sighignola summit on the Swiss border offers views so breathtaking it's been named one of the most beautiful places in Italy.

This private island is still in the family after a 400-year history including a witch hunt and a pirate.

Art Deco and “Wrenaissance” mash-up, this recently restored royal residence has been home to kings and comes with secret monkey passages included.

The main gates have been locked since 1745 and will remain so until the Stuart Dynasty returns to the throne.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

Obscure Freemasons still live in D.C.’s largest private residence.

A blend of art, antiquities, and Americana fill this museum, surrounded by whimsical, enchanting gardens.

An extraordinary "City of Caves" carved from solid stone.

Tucked in Mumbai’s wealthiest neighborhood is one of the city’s oldest and most sacred sites: a temple complex believed to house the waters of the Ganges.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

Treehouse motel and treehouse-building school.

Home inspired by the crystal rock formation of the Emerald Estates.

This egg-shaped treehouse was inspired by "sport sleeping."

What began as an art installation is now the private drinkhaüs for a brewery's employees.

A whimsical village of unique treehouses resides in a Washington forest.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.