Nashville: Percy Warner Park
Percy Warner Park is my go-to hiking place right now. The white trail (designated by white trail markers) is probably the easiest and quickest. But you could make up your own. (Go to this link for more information about the trails.)
When Lisa and I came here for the first time, I drove around and around this park trying to figure out where we were even supposed to start. Do not use Google maps to find this place. It will lead you to some top of a hill that's not really a place to park nor really exists. Lisa and I drove through here for thirty minutes wondering where to get out. Percy Warner is a very large park when you don't know where you are. I recommend parking at the Belle Meade entrance next to the golf course off of Old Hickory Blvd. Location here. You can start with the stairs. They're not as bad as they look... kind of.
If you're feeling spooky, go here at night and drive through it and tell scary stories. I was thoroughly freaked out.
Or, you can legitimately go on a night hike here. See the Nashville Hiking Meetup group for more details on when they go and some other cool places to hike.