The Daily News has a big feature on underground tours of the city's underbelly of tunnels and sewers, as led by Steve Duncan of What's great is the quote from the Department of Environmental Protection's spokesman: "They are not allowed in our sites. As you can probably imagine, we do not approve of unauthorized visitors. These are dangerous places. I only hope whatever they're doing, they're being very, very careful." And not carrying suspicious backpacks! Authorities freak out about the groups, and we can imagine some people had a case of the vapors when reading the story, but people have been exploring supposedly inaccessible parts of the city forever, whether it's a trip to the Highline or an organized tour through an old tunnel.

What are your favorite urban explorations thus far? Another urban exploration group is the LTV Squad, and there are urban exploration groups all over the world on MeetUp. And Forgotten-NY's Kevin Walsh organizes periodic tours for parts of NYC that aren't necessarily hidden but places we take for granted.

Photograph by Mike Epstein at Satan's Laundromat