I really like the idea, where would we be building it? In the old world I was going to build a darkened crypt that'd spawn mobs, you'd try to run through it, and get the treasure at the end. I'd also really not like to do something like the Ember Battlefield, that'd take forever. (Mob spawner spawns mobs, brings them to one area for battle, w/e)
I would like to build it somewhere a lot of people could see it, but there's not really a place a lot of people see daily other than spawn. Decorating spawn would be fun, but I want to build something and I doubt Asy would give me spawn perms. So I will most likely be building this in Helrune. A Halloween style obstacle course sounds like quite a good idea. I could invite anyone who wants to do it to Helrune I guess.