Is it safe to climb? Only one way to tell.

Although it does at least look potentially structurally safe. The benches and chairs have been attached to each other in such a way that, as long as that strange green glue is strong enough, should be secure.

It is certainly holding up Link's weight okay. Doesn't even wobble, as he stands at the top, and waits for Donnie to climb up. Maybe even lend a hand, once Donnie is close enough.