When you visit Yosemite Valley, you really can't help but see Yosemite Falls. But you really ought to take the time to take the walk up to the lower falls - it is just too easy of a walk. On the other hand, if you are up for a real challenge (which we weren't :-), you can take a trail to the very top of the upper falls.
Here are a few photos of the short easy walk to the base of the lower falls. The path through the grove of trees, the distant view of both the upper and lower falls, and a pair of views of the lower falls.