i have been up to the paulinskill viaduct twice. it up off route 80 in north jersey. its a old abandonded train bridge. it was built in the early 1900's and at the time was the biggest bridge of its time. i think that only lasted a few months though. you can climb up into it and climb through the arches. its not really scary or anything just strange that its abandoned and is in the woods. i think its about 100 feet tall. its cool heres a link:
http://www.xydexx.com/modernruins/paulinskill.htm
i just read that link. we went all the way to the other end of the bridge through the arches. i think there was 6 or 7.