Sometimes one wants to escape from the city... go upstate to the Catskills, Adirondacks or leave for warmer more remote climes... or some just go underground. Three guys spent five days traveling through four of the NYC boroughs all underground, using only tunnels, subways, and sewers. I see a Hollywood writer thinking about a proposed film where a meltdown at Indian Point nuclear power plant makes being above ground too dangerous. So a group of people trying to make their way to the furthest tip of Queens ( to find loved ones of course) use only the underground network to travel out of the city. Actually not to bad, but would have to do a bunch of fact checking...
The guide on this five day exploration has a pretty great website with videos and amazaing photos. It's reassuring to see being a bit insane can actually be fun.
Undercity

Explorer Walks From Bronx To Brooklyn, Underground CBS New York – News, Sports, Weather, Traffic and the Best of NY

This past Christmas I went to a more accessible ruin.. Dundenberg Mountain up in Harriman State Park. The site was going to be a railroad leading to a hotel at the top of the mountain at the turn of the last century.. but the developer ran out of money. The train trip was actually to go through the mountain at certain points via huge tunnels... most never got finished.