Fossil Creek
To get to Fossil Creek, you can park at the Trail 15 Trailhead and ride through Strawberry down Fossil Creek Road. Go past the Bob Bear parking lot, all downhill, until you reach a barrier. Go around the barrier, and keep riding downhill about 4 miles to Fossil Creek.
The road is old and semi-maintained, there are often big rocks in the middle of it, and if your brakes fail, you are in a lot of trouble. I would not take a beginner down this.
The views are absolutely spectacular, and Fossil Creek is one of the most magical places I have ever seen. It is difficult to get to, which makes it even more special.
You also have to ride back up, about 8 miles back to Trail 15. The way is in full sun so plan accordingly.