Even though 4 days is best, just one day in Yosemite is worthwile and can be a great visit.
Where to stay
Bass Lake and Sugar Pine are also near the South Entrance
Mariposa Grove of Giant Sequoias
Small visitor center and easy trails through the giant sequoia trees
Wawona History Museum, covered bridge and historic art studio
Beautiful stream and living history in the summer
Glacier Point Road
Hub for hiking and epic views over the Yosemite Valley
Sunset at Tunnel View
Perfect view of Yosemite Valley as the shadows take over
For this and more ideas for single day plans in Yosemite National Park read the full article.