The Subway is one of Zion's most famous places and it is also one of the top sites for photography in the park. Although it is so famous there are usually few people around because it is a very long hike in and the traffic is limited. The hike is about 10 miles round trip and is very strenuous. If you want to do the hike you will need to reserve a Zion backcountry permit. The hike is a bit technical and for the most part there is not a well defined trail. You basically follow the river once you are down in the canyon.
After about 5 miles of hiking you will get to the Subway portion, which is actually quite short. It is named for the tunnel like formation of the cliffs, see the image at the bottom of the post.
The image with the pools was a pretty straight forward composition. I wanted the lowest pool to be in the lower third of the picture to add foreground interest. The cascade of pools provided a great sweeping line that gives the image depth.
As for the more technical details of the shot, I had a polarizer filter on my lens and chose the small aperture of f/13 so I could get the long shutter speed that would give the water a very smooth look. For post processing I took down the highlights a little, gave saturation a slight bump and sharpened it for the final result.