Airport Pits off of Leitrim Rd.
Nothing crazy technical, lots of soft sandy landing areas for those inevitable spills and a good place to practice slower speed drills. not a huge amount of "trails" but enough to make it interesting. Just be respectful of other users like dog walkers, runners, bikers, etc.
Great for those days when you only have a hour or two to get out and don't want to do a ton of slab to get offroad.