I've been spending a little more time than most people looking at or into unused tunnels of Brooklyn and I've discovered that most of these tunnels lie dormant, ignored and probably forgotten and information and access is often difficult to obtain. Fortunately for all of us, there is one very loved tunnel, originally built by the LIRR that lives under Atlantic avenue in downtown Brooklyn. Claimed to be the oldest train/subway tunnel in the world, built in 1844(!!) and (re)discovered by Bob Diamond in the 1980's, Bob gives tours inside the tunnel twice a month. Bob tells his amazing story (several acts long) inside the humid and atmospheric tunnel. Anyone and everyone who gives a slight hoot about history or construction should go on this tour. Well worth the $15. (Bob runs the the Brooklyn Historic Railway Association - where you can find info on the tour.)