The plan was to use a rope ladder to get up, but my 4 year old struggled with the transition to the platform, even though he could climb it just fine. So we vetoed it, even after making a pretty nice ladder. I leaned a couple of 2×4s against the entryway, cut the angle, and nailed on two thicknesses of cedar board all the way up. The plan was to put climbing holds up a wall, but I ended up just cutting foot/handholds instead. I'd like to say this was free, but I wore out a big spade bit cutting the holes - it got too hot, and bent. This job was easy if a little time consuming to do - mark and drill two big holes, mark a line between them at the bottom and an arc at the top (I used a plastic bucket) and cut out with a jigsaw. This had really rough edges, so I rounded them off with my little router. That worked great, so I went around quite a few other edges on the treehouse with it. Smooth!