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Light colors: lower level
Dark colors: upper level
blue: water
yellow: stone
red lines: teleporter
green lines: alternative teleporter target
blue X: switchable sink/source of water flow
brown X: (maybe) fish basin
The color of teleporter indicates on which level the teleporter is located
1: Invisible Spell
2: Energy Drain Spell
3: City of Bones: if you change the direction of the current it will change back as soon as you go over the waterfall. So you never get the chance to enter the teleporter with alternate target.
If you try to run through the teleporter, you won't get to the other side, but the map is marked as visited and you can quick travel to the other side. You still cannot climb the waterfall as the water is always traveling downwards.
If you come back later with your full group, you can place one member at the waterfall or teleporter. With another member switch the current direction.
Room NW is not reachable according to info from devs.