Four-story concrete hotel never opened to customers.

The king of U.S. high points towers over every other peak on the continent.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

Live a night as a Byzantine King, with a minibar and private jacuzzi.

This ancient subterranean megalopolis is known for the hot oil traps that were installed above each of its entrances.