When I lived in Brooklyn, I had heard rumors of a "secret tunnel" not more than two blocks from where I lived. It was supposedly an old railroad tunnel built to run dozens of blocks underneath Atlantic Avenue, making it (effectively) the first subway in the world.
Unknown to me at the time was that the secret tunnel was more than a mere rumor. Several years earlier, an interpid teenager, hearing the same rumors, actually went down a manhole on Atlantic Avenue and discovered the tunnel.
The tunnel was built in 1841 and abandoned in the late 1850's. After its disuse, it was supposed to be completely filled in. But the less-than-honest contractor hired for the job merely plugged up the ends of it, and capped the holes leading to the street. Very few knew of this of course, and years later the tunnel was forgotten.
At 17 feet high, 21 feet wide and 1,611 feet long, the Atlantic Avenue tunnel purportedly holds more than empty space. It is believed to contain within its walls, the bones of a tunnel building supervisor, who was shot and killed by Irish laborers after informing them that they had to work on Sunday. Others have written that the tunnel contains pages from the diary of Lincoln assassin John Wilkes Booth. Six blocks of the tunnel — almost half its length — are still blocked off by a large brick wall, and many believe that an actual British locomotive may lie on the other side. (Plans to break through the wall are slated for this year).
Tours of the tunnel are rare — once or twice a year — but the tour guide is Bob Diamond, the teenager who "re-discovered" the tunnel in 1980.
A nice little story of modern-day archeology.
For more info, read here. Or watch this, from the upcoming documentary, What's Behind The Wall.