Tenaya Canyon is the most dangerous place in Yosemite Park, judging from the
number of people who died while hiking in it.
As the condor flies, it is about 15-16 kms of cross-country hiking from the Sunrise trailhead at Tenaya Lake on Tioga Rd to Mirror Lake in Yosemite Valley. But it takes a whole day.
Start at the Sunrise trailhead on Tenaya Lake. Leave the trail as soon as it starts climbing. You are on the left side of the creek (as it flows down). Cross over to the other side when you can. After about 40' you will see the sign that tells you to go back. After about one hour of hiking, you reach the famous bowl. At the bottom of the bowl there's a forest. After the forest you reach the Pywiack Cascades. The only way that i found to get around them was to turn right (west) and head for the side of Mt Watkins. A tributary comes down from that side. That tributary is relatively easy to hike down although still a very steep descent. The problem that you can already see ahead is the next gorge. If you are lucky you will meet someone with rope that will help you down. When you reach the bottom of this tributary, after another short stretch of forest, you have to climb down this gorge.
In order to avoid all of this, i basically climbed Mt Watkins, then came down where the Watkins Pinnacles are. But i wouldn't recommend this route as it is very time consuming (i basically summited Mt Watkins) and still deadly dangerous. It is wiser to go to the gorge and wait for a party with rope. From where i was, it looked like one could risk his legs and go down without a rope, but i did not try it out.
I hit the canyon again passed the second section that people mostly rappel down. Now there is a series of cascades that can be relatively easily hiked down. Just be extremely careful when you are walking on wet granite. Granite is slippery enough when it's dry. The canyon becomes very shady inside a forest. I could not make out how far before or past Half Dome i was. I only had glimpses of the mountains around me and couldn't recognize them from that angle.
There is reportedly a used trail on the right handside of the creek but i never found it. I walked mostly 10-20 meters from the water to enjoy the countless pools and cascades. At some point my main problem became poison oak. The closer to the creek, the less poison oak, so i was bouldering most of the time.
When you have to cross a tributary coming down from Mt Watkins on your right, you are five minutes from the end, so move towards the creek. In a few minutes you will see the bridge. The bridge is part of the loop around Mirror Lake. Trails take you anywhere you want to go, or head for the Mirror Lake shuttle bus stop. It took me about nine hours from Tenaya Lake to the shuttle bus stop (15/16 kms).
I would not recommend this hike. Besides being very dangerous, it offers very little that you cannot see when you drive on Tioga Rd. The waterfalls are pathetic compared with the more famous waterfalls that you can see in the valley. The creek is not particularly impressive compared with hundreds of similar creeks that i have seen in the mountains. There is really no other reason to hike Tenaya Canyon than its deadly reputation. Rock climbers probably get a kick out of those short rappelling sections. Personally, i found them rather pathetic (both the sections and the rock climbers).
By far the best view of the day was the picture i took from almost the top of Mt Watkins (above the canyon, looking straight up to Half Dome). If you are inside the canyon, you miss 90% of the show.