The deepest metro station in the world.

Liechtenstein's royal family calls this medieval alpine castle home.

The castle still holds traces of the abandoned Roman fort it was built atop.

Dozens of musicians have planted trees in this Danish park, and donated songs to go with them.

A crumbling cathedral condemned by an earthquake.

In Costa Rica's cloud forest, the roots of a woody ficus create a botanical bridge.

The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

Moscow's other, lesser known kremlin is a fairytale-like cultural complex modeled after Old Russia.

Legend says this sacred tree was a gift from goddess Athena.

An ancient octagonal weather station named for the eight Greek gods of wind.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

Skyscraper powered by wind turbines attached between its towers.

A preposterously luxurious hotel with gold-plated iPads, Rolls Royce chauffeurs, and a staff that trains by watching "Downton Abbey."

On any given day this sprawling market houses literally tons of government-regulated gold, gems, and precious metals.

This indoor ski resort has a mountain contained inside a mall.

A faithful reproduction of Al-Jazari's enormous water clock.

This artificial archipelago was supposed to resemble a map of the world.

This museum housed in a former brothel explores the past and present of sex work in Amsterdam.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

The oldest monument in Marrakesh and the city's only surviving example of Almoravid architecture.

Deliberately hidden for centuries, the magnificent Saadian Tombs were eventually uncovered in 1917.

The largest madrasa in Morocco once housed more than 900 students within its exquisite walls.

Fortune tellers, snake charmers, poets, and storytellers all gather on this historic square in Morocco.