I think one of the highest places you can go is the top of the lost precipice gh we built a ramp to the highest mountain in lost precipice and its really high (without void jumping)
we did the same thing with a cloud staircase in gilded hollow! got so high we couldn’t jump without hitting out heads at the top of the map. but as far as natural structures, I’d have to say The arm of abbadon is pretty high. I can glide from one end of the map to the other