Derinkuyu Underground City

Derinkuyu Underground City was built by Christians to escape religious persecution during the fourth and seventh centuries. A UNESCO World Heritage Site, the city is a maze of underground corridors and rooms. Visitors can only see 10 percents of the city, which could accomodate up to 50,000 people. The city is even connected to othe underground city via a narrow tunnel. But perhaps the most astonishing feature us the enormous defense door that only opens from the inside.

                                                                         
article & pictures from:
http://www.neungyule.com/pages/ko/  sometimes-interesting.com
www.theexpeditioner.com  www.goreme.com