The Homestead Trail in McKinney Falls State Park is the best trail in the park for hiking and mountain biking - at three miles long, it is not too long, but it is a lot of fun.
Part of the fun of the Homestead Trail is getting there. The parking lot is on top of a small hill that leads down to Onion Creek across what looks like the surface of the moon - no vegetation grows on the rock here. You will need to cross Onion Creek, because the trailhead is actually on the other side of the creek. The trail is a loop, and can be a little hard to follow.
The trail is great for mountain bike beginners - not too long, not too short, and not too technical - it makes for a fun but challenging first ride. Expert mountain bikers will be bored though. It also makes for a great place to do some basic trail running.
This trail turns into a muddy mess with rain - if you want to hike something fun if it has been raining a lot, drive another thirty minutes to Bastrop State Park - it drains a lot better than McKinney Falls State Park.