Half Dome Loop via John Muir Trail
Half Dome is the ultimate Yosemite day hike - the one you can't die without doing, and the one you're most likely to die while doing. The hike up this Yosemite icon features incredible mountain and valley views, wildflowers, waterfalls, old-growth sequoias, and fascinating glimpses of some of California's most dynamic geological history. The hike begins at the Happy Isles Trailhead and goes by Sierra Point, Vernal Fall Footbridge, Clark Point, Nevada Fall, Little Yosemite Valley, Silver Apron, Emerald Pool, Vernal Fall, and Mirror Lake Trail. The trail leads to a junction with the Mist Trail and John Muir Trail. Take the JMT as it forks to the right for a slightly longer, more gradual, and dryer route to Half Dome. As you hike higher, the views of Half Dome, Liberty Cap, Nevada Falls, and the Yosemite Valley just get better and better. The trail leads to the top of Nevada Falls, where you'll cross over the Merced River, and after a quarter mile the Mist Trail meets back up with the John Muir Trail. From there it's 1.1 miles to Little Yosemite Camp and another 2.2 miles of climbing up to the Half Dome Trail junction. Once on the Half Dome Trail, it's just another 2 miles until you reach the summit. Right before leaving the comfort of the shade from the taller trees you'll be greeted by a park ranger who will check for your permit. The last half mile is fully exposed to the sun, and the climb begins in earnest as you make your way up the carved out granite stairs. Making your way up the cables can easily take up to an hour, depending on how many people are making their way up and down. Once you're on the summit of Half Dome, you'll have beautiful 360-degree views of the Sierra Nevada, making all your hard work worth it.
Parking - Your closest option is the trailhead parking lot. It's just past Half Dome Village, on a road that's marked "Service Vehicles Only". However, your private car is apparently allowed to enter this road to perform the service of getting you to the trailhead parking lot. The trailhead lot has a few dozen bear-proof storage lockers in which you can store all the scented stuff you don't want to haul up the trail with you. They tend to fill up early, though.
If the trailhead lot is full, you can park at Half Dome Village, which you'll find near the east end of Southside Drive. As you head east into Yosemite Valley, you'll find road signs pointing the way.
When to Visit - You can't climb Half Dome unless the cables are up, which is generally from late May or early June through Columbus Day weekend in October. The waterfalls will be better the earlier in the year you go. Avoid Half Dome on days when there are thunder clouds in the area - it's not worth the risk. Even rain without lightning will make the granite on the cable route dangerously slick, so it's best to skip stormy days altogether.
Permit - You will need a permit to climb Half Dome. The park service only issues around 350 permits per day for the cable section (225 for day hikers via the March lottery, 75 for backpackers, and another 50 or so given out via lottery two days in advance), and not all the permit holders show up, so there will usually be less than 350 climbers. The best times to go are weekdays and the months of September and October, as there are less people trying to climb.
Definitely a no for children. The granite face is slick and steep. Child Rating is 1.