This 8-mile section of the old PA Turnpike was abandoned in the late 1960's. The pavement is now cracked, overgrown, and it feels lonely and dead. But it's actually fun to ride on!
We met a group of folks from Bikeforums.net at the access point. There's a sign before you enter that, in effect, lets you know you're riding at your own risk. In fact, I wasn't entirely clear on whether riding here is legal or not.
There are some tunnels, so bring a light along. (One tunnel is about a mile in length.)
The pavement is very rough, and I'd bring a bike with wide tires is you have one. I was surprised by how few mountain bikes I saw:
This is more of a stroll than a ride; you really can't go that fast, or that far--but riding on what used to be the Pennsylvania Turnpike is a strange experience, and one I found well worth the drive from New Jersey.