Yosemite has to be seen to be believed. Photos cannot possibly do it justice. Granite monoliths rise above the valley floor calling one to climb and explore. If you are in good physical condition, embark on a strenuous hike up to the top of Yosemite Falls. It is 6.6 miles round trip. Even if you only make it half-way you will get awesome views of Yosemite Valley, Half Dome and Lower Yosemite Falls. When you look down from the top you'll feel you're in a Road Runner cartoon. Bring sunscreen and plenty of water as there is little shade from the half-way mark on up.
Another great hike is the trail to Vernal and Nevada Falls. It also is strenuous and 6 miles round-trip. But you get up-close looks at massive waterfalls.
If still want great views without the hiking, there are two must-see viewpoints. Tunnel View on the west end, and Glacier Point overlooking the valley from the southeast. Tunnel View is the classic view Ansel Adams made famous in his photographs. Get there an hour or two before sunset for the best photos. Directions from the park: Take the HWY 41 exit to Wawona or Fresno. There is parking at the tunnel entrance.
Glacier Point Road is open only in the summer. It offers an up-close look at Half Dome and bird's eye look at the valley and waterfalls.