Serpentinas Trail Blackwater Forest NW FL. Wife and I had a great ride in awesome weather (around 76 & mostly sunny). Excellent little trail if any of you are ever around this way
Edit - I've received quite a bit of interest in this so after the pics I'll share the background info.
In 1942 the worlds first nuclear reactor (CP-1 or Chicago Pile 1), located under the bleachers of Stagg Field at the University of Chicago went critical creating the first self-sustaining nuclear chain reaction. It was the start of the Manhattan Project - the United States attempt to develop the first atomic bomb.
A couple months after the reactor went critical, they thought in might not be a good idea to have the only active nuclear reactor they wee attempting to waeponize sitting under the grandstand at a college in the middle one of the largest metropolitan areas in the country. It was disassembled and moved about twenty miles outside of town (cause that would have saved everyone if SHTF) into the Manhatan Project site at Red Gate Woods in the Palos Forest Preserve. It was rebuilt with some upgrades and renamed CP-2 and became a military gaurded secret. The whole area was guarded by Army MP's, no one was allowed in, and no one was told why. Eventually they built CP-3 there as well.
In 1956, the Manhattan Project facility was demolished and CP-2 and CP-3 were decommissioned. The researchers moved to what is now Argonne National Laboratory but there was a crap load of radioactive nuclear waste at the old site... the nuclear fuel got shipped down to Tennessee, but the reactor and the buildings, the dug a massive hole, tossed it in, buried is in concrete and laid dirt over the top of all of it.
In the mid 90's 35 acres of the forest preserve was quarantined after an inspector found a chunk or uranium barely at the surface, further testing found a whole bunch of radioactive and toxic **** in the ground. They spent 5 years and a few million dollars cleaning it up before it reopened. The nuclear reactor is still buried beneath that grave stone and every year inspectors come to test the ground and well water pumps for contamination. There was an article I read a few years ago about the levels of radioactivity in the well water being deemed "safe" by inspectors who refused to drink it... go figure.
Every year my local (until I moved) mountain bike advocacy group does the "Palos Meltdown" mountain bike race. It's the only large good trail system in Chicago area (probably because they can't dig there to add buildings or anything). Along the single track there a little gap in the trees, looks like doorway, that opens to a small field with that nuclear grave stone in the center.
Google will find you plenty of info if you want to know more.