Fisheyes & Sun Flare
In Yosemite National Park there are plenty of reminders to look up. Half Dome, Glacier Point, and numerous waterfalls just to name a few. There is also, of course, the forest and the trees. Using a fisheye lens (in this case a 10.5mm) while looking straight up creates a unique view. Since the lens will cover most of the sky there is also the likelihood that the sun will be in the frame.
By stopping the lens aperture down to a high number (small opening) and hiding most of the sun's light behind a tree, you will create a natural sun star without the need of any special filter. You may also find some extra, colorful reflections across the image (notice diagonally down toward the lower left corner of the image there is a green circle). This is a result of the bright light directly into the lens.
Sometimes you may wish to avoid this, other times enjoy the unpredictable nature, of nature. Another advantage of finding a subject where you are pointing the camera directly up; you won't photograph your feet! If you have ever thought about the possibilities a lens like this can bring to your photography, but you don't want to invest in such a special purpose lens, consider renting one for a few days or even a week. That's what I did before I decided the investment was worth if (for me and my style of images). There are several local dealers that rent lenses and even cameras.