I am a big fan of South Mountain. This is my fave place to hike/trail run. I can literally spend all day exploring new trails. Many of the trailheads are 10-15 mins driving distance from me so that is perfect for a quick hike/run and when I have more time it's nice to drive out a little further and try out some new trails. Some of the trails can get a little crowded on the weekends when the weather is nice, but I do a lot of my hiking/running at sunrise in the winter and in the afternoons in the Summer so I am usually all alone. :)