Lower and Upper Yosemite Falls
Year round destination. Best in May and June when the waterfall is at its peak due to the melted snow. Temperatures are perfect for hiking. July and August crowded. September is nice as well.
End of summer the waterfall is a trickle only and the park is completely crowded. Sometimes even the park entry need to be closed. For the 12 km hike with more than 800 m in elevation I advise to start early in the morning. We didn't meet anybody on the whole trail which leads to the top of the highest waterfall (739 m) in North America. The view from the exposed plateau to the valley, Half Dome, The Three Brothers Rock and El Capitan is stunning. The Yosemite Creek which feeds the impressive waterfall has a very cold temerature from melted snow at the end of May.
Yosemite; world's first National Park protected since 1864, designated as National Park in 1906 and Unesco World Heritage Site since 1984. One of the most popular parks in the US. If you want to stay inside the park book it as early as possible. Same for the hike to the top of the Half Dome. One of my favorite hikes in the world.
More information: http://www.nps.gov/yose/planyour...