You can see under the stairs (and through the map) by looking under all of the stairs in the inner tube river.
Edit: This is still the case even after 0.18.1.1’s mentioned seam fixes around the Plaza.
Steps to Reproduce
Go to the river, jump in the water, look at the stairs.
What I expected to happen
Stairs to go all the way to the ground so you can’t see under them and through the map.
