The Subway (Bottom Up)
From the Bottom: 2B III 
Getting There
From Zion Main Canyon , drive south on Highway 9 to the town of Virgin , and turn right on the Kolob Reservoir Road . The well-signed Left Fork Trailhead is on the right 8.1 miles from Virgin.
A less ambitious hike, and a lot easier carrying significant photogear, the "From the Bottom" hike still requires a permit and is not for wimps. There is no established trail, and many stream crossings and rugged rock hoppings are required to get to the Subway. If it is hot out, it will be scorching, though a healthy stream offers some relief. There is a hidden spring on the left side (North side) of the canyon about a half mile from the Subway, below the red cascades.
When you arrive at the Subway, you will be quite grateful for the shade and coolness. A tripod and drybag will assist in taking good pictures. The first obstacle in the Subway is surmounted by swimming two pools, then bouldering up on the right side ( or a boost would probably do it ). Be sure to duck into the alcove under the waterfall before heading upward. Another quarter mile of very scenic Zion coolness can be explored before a waterfall blocks further access.