In North Graal City where the railroad used to enter, there's a weird cave thing, in one of the rooms is an empty chest and a totem pole in a pond thing. just wondering what it is  

It's a cave.

A cave with a cool waterfall slide though D:  

well as long as theres a slide  

This is a really old level that you used to be able to access from that small building on the cliff above revolution, well, if you offmapped, that is  

I think they rerouted that cave because I remember going in it when they had that out of the map rock glitch and it led to that house on top of the cliff.