Teleportal Room:
A 10-foot-diameter hole, ornately edged, gapes in the floor of this room. Directly above it is a similarly sized hole in the ceiling. A small pedestal sits
against the southwest wall, a diagram barely discernable above it. There are three small bowls on the pedestal. The bowls are empty.
The hole in the floor and ceiling appear to lead down to an identical room below and above, and those rooms to identical rooms below and above, ad infinitum. It is like looking into the infinity of two mirrors facing each other.
Each level is 15 feet. You discovered that there are only three levels, each color coded. So dropping something down will make it fall through the infinite teleportal and really fall only 45 feet before returning to where you dropped it.
Your level has a black ring around the hole,the one below you is red, and the one below that is white. Looking up, it appears that the one above you is white, and the one above that is red. The only difference between the rooms is the placement of the southern door on one of the rooms and the color of the ring around the hole.
Below is a diagram. They are supposed to be all the same size, so ignore my error. You are at 20a; you can reference the others by 20b and 20c or by color of the ring.