From Hoosier Pass, south of Breckenridge on Colorado 9, go 7.6 miles north to the well-marked Spruce Creek Road. Turn onto the Spruce Creek Road (look for a sign that says "The Crown," and follow it for approximately 2 miles to an obvious parking area. This is the Spruce Creek Trailhead. Park here with a two wheel drive vehicle.
4 wheel drive vehicles with high clearance can proceed much further. Go past the obvious parking area, and come to a Y in the road. Take the right of the Y. Soon you will come to another Y, and again, you should veer right. When you make this right turn, you will be passing through an open forest service gate. Go past the turn for Francie's Cabin, one of the 10th Mountain Association Huts, and continue up the road past treeline. After 2.3 miles, you will arrive at the Lower Crystal Lake. This is as far as you can drive.
There are several pullouts along this 4x4 road if you decide to bail out and walk the rest of the way. The worst section is near the middle where a number of large rocks line the roadway. A standard 4x4 should be fine for the road, but I wouldn't try it without skid plates.