Arlington off of SH360, just south of trinity blvd on the right of 360 just before the rail bridge. There spot there that goes pretty deep around that area. You can cross the train tracks and find trails all around. Watch out for dirt bikers, ATVers, trains, and ect. Usually theres a few pickups and jeeps there, I think you'll even discover a vehicle or two that didn't make it. The area is under control of the city of Fort Worth, but it's so far off their normal jurisdiction area that usually only emergencies bring the po-po and the fire department out there. I've seen the occasional white fort worth fire truck out there though.
from: 32.837265,-97.04494 to: Angus G Wynne Jr Fwy/TX-360 S @32.818390, -97.059770 - Google Maps
If you study this map you can see that if you cross the tracks (either over, or under the bridge, don't die or get stuck here) you can find a route to the bridge that goes over the river, you can cross under that bridge and find all sorts of stuff.
Again, if you go here: be careful near those tracks, theres a TRE station right by this spot, and no rail crossing, therefore trains are always imminent and they don't blow their horns unless they see you. Most people cross under the bridge on the side of 360, but it's narrow so be careful.