From the Four Mile Trailhead on Southside Drive, head up Four Mile Trail to Glacier Point. Cross over to Panorama Trail and follow it downhill, crossing Illiouette Creek bridge at about 12km. Continue following Panorama Trail until it meets an intersection with John Muir Tral. Turn right onto this and cross the Merced at the top of Nevada Fall.
A short way after the crossing, at the next trail intersection, turn left to stay on John Muir Trail, which you stay on, climbing, until you come to the trail junction with Clouds Rest Trail. Turn left onto Clouds Rest Trail and countinue climbing. You'll start to feel the altitude as this trail takes you all the way to the summit of Clouds Rest at 3028m, which has the most spectacular 360 degree mountain views you could imagine.
If you can tear youself away from Clouds Rest, head back down the trail, back onto John Muir, retracing your steps all the way back to the intersection with Mist Trail (stay left and don't re-cross the Merced). Follow Mist Trail, which takes you down past Vernal fall, and gets its name from the water spray that soaks you from the waterfall as you steeply descend the famous stone steps (they are smooth and slippy from all the water, so take care).
Keep following the main trail, heading towards Happy Isles Trailhead. At the road, turn left and make your way to the parking lot opposite Upper Pines Campground.
