Day 1: Happy Isle Trailhead - Liberty Cap - Diving Board
Day 2: Diving Board - Happy Isle Trailhead
There is a trail called "Snake Dike Approach". Do not follow the trail unless you are a rock climber with climbing gears. It can be too sketch for hikers.
About 0.2 miles after Lost Lake, follow the cairns going down about half miles then going up. Although it's quite steep, it's a safer route than "Snake Dike Approach".
You shouldn't rely on the Alltrail map that I linked here as I drew it based on my memory. But you will get the idea where you can find the cairns.
The water in Lost Lake was not clean. Merced river was the last reliable water source. We had lunch near Merced river and took 3 liters of water.
We camped at the edge of diving board as it was only place we could find flat spots. No camping spot was completely flat. But we could find more than 4 reasonably flat spots to pitch our tents.