there could be more than one, but in Raco, Michigan, there is the old military airport there. they used to have surface to air missles and what not in underground silos that were meant to protect the sault locks during the cold war and what not. it's a huge triangle, each side probably being around a mile long, with straight aways connecting the sides of the triangles and huge square/rectangle area's also. it's all concrette, not used by the military anymore, acutally used by car companys to test cars in the winter. they have a seperate track nearby, they don't use the concrete runways that much, since they have black top straight aways bulit nearby for testing. it's off of M-28, west of I-75, about a 15-20 minute drive. there's no signs up about tresspassing or anything, but there's bulidings there that are used by the car testers. i've been there many times in the middle of the day, there's no one around, and it's a blast, but you have to go in spring/early summer, cause it's not maintained and grass grows up in spots. it's in the middle of the woods, so you can't see it from the M-28, but you can't miss the entrance, cause there's gates there, but they're never locked unless there's testing going on (gotta keep the new cars top secret, though they take them to sault ste. marie to get worked on if they don't have the right stuff with them, i seen the new mustang in the spring at the ford dealership, and lots of SRT-10's last winter going to the chrysler dealership). i'm sure it's probably illegal to be out there racing and stuff, but i've been doing it for the past 4 summers and never got in trouble. there's even people who camp back there with 5th wheels and stuff. it's about an hour drive total from the bridge if anyone was wondering how to get there.