First things first, The Barton Creek Greenbelt is considered the seventh best hiking trail in Texas. My favorite trail is a 7.25-mile (11.67 km) stretch of public land that begins at Zilker Park and stretches South/Southwest to the final section commonly referred to as "The Hill of Life" which ends in the Woods of Westlake subdivision.
The beautiful limestone cliffs, dense foliage, and shallow bodies of water with entertain your eyes as you jump over fallen tree trunks. There is the occasional snake or Armadillo sighting, but for the most part you will be speeding past pack of deer busy scavenging for food. Year long you will be sharing the trails with hikers and bikers, so don't get too lost in your Zen. During years of heavy rainfall the water level of the creek rises high enough to allow swimming; the perfect way to cool of after a tough run. Bring your trail running shoes and take to the trails...it's another world out there!
If you are curious, but you don't wanna go out there alone, join The Hill Country Trail Runners during their training runs and experience running in a slightly muddier, yet fun way. For more info: http://www.hillcountrytrailrunners.com/