Walking tours allow visitors to get intimate with their destination. Some of the coolest (and perhaps creepiest) are underground walking tours. These underground tours sort of let you in to secrets of the past, mysteries, and wonders not all people get to see. Here are some of the best underground walks you can find across the globe, as presented by Journey etc:
Cold War bunkers of Berlin, Germany are said to be radiation proof. This bunker can house around 3,500 people and operate for two weeks given all the supplies were provided prior to a nuclear attack.
The tour of The Catacombs in Italy will take you underneath Rome and give you a peek to the birth years of Christianity. As you walk in this underground community, take note of the centuries old graffiti which are mostly prayers.
This is the dirty side of the City of Lights which, ironically, helps keep everything clean. The sewers is about 2,092 kilometers long where millions of gallons of water rush through everyday.
View the rest of the list at Journey etc.