M.R.
My 3 year old just got one for his birthday and I was hesitant to put it up because I didn't want it to ruin the wall. My hubbie took charge and put it up in his room. Turns out it's stuck to the wall with those no damage 3M things. My son loves it and has lots of fun with it. I'd recommend it for sure now.
p.s. - I took it down b/c I didn't like where my hubbie put it and there was no damage to the wall or any indication it was there. I just bought some more 3M things and moved it, so it's not permanent by any means.