We took several days of vacation in Yosemite in the early 1990s and I made the round trip from Camp Curry to the top of Half Dome one day. I was in 33 minute 10K shape at the time. I ran every part of the distance that it was possible to run. The first problem I encountered was a guided mule or horse tour on the way up to Nevada Falls. The guide said that I was not allowed to pass them on the trail, so I cut across a switchback to get around them. My next problem was that I couldn't find the water source that a Yosemite hiking guide said would be available on the way from Nevada to Half Dome. But that wasn't a problem at the time. If I were to do it again, I would carry and stash some water for the return trip. The running turned into hiking when I got to the rocky section on the way to the base of the cables. The sight of the other people already climbing was almost comical. There were maybe 8 people total. They would move a few steps up, then stop. Move and stop. Someone at the base said that I should get some gloves from the pile that were there. I did and the ascent was easy for me, but I was careful to be very deliberate on the cables because you don't want to fall. It would be safer to have a harness and a couple of tethers with carabiners to clip on and off the cables, but that's looking back. At the top, I walked around for a few minutes, then noticed some people sitting near the edge of the front wall. I got on my hands and knees and approached them. Some of these people had their legs dangling over the edge of the 2000 ft drop - I couldn't believe it. I inched to the edge and looked over and that was good enough for me. Then it was time to go back. The return trip was not too difficult, but I was getting thirsty and a very kind woman offered me a sip from her water bottle as I neared Nevada Falls. I did have very sore achilles tendons for several days afterwards, and regret that I didn't take a camera with me.