Depicting a three-dimensional world using the limits of the NWN engine is complicated. And although considerable thoughts has gone into different areas and how they match up, one thing that is particularly tricky to depict is elevation - particularly as despite appearances some caves/mines slope up or down and there can be large "ramps" in between transitions.
In the interests of clarifying things, here are some notes about elevation:
Major EFU Underdark Landmarks from Highest to Lowest:
The Top of the Spire
Dunwarren Gate
Abandoned Mines (which are not really flat but are rather sloping down to the Lake Shore dramatically)
Upper Sanctuary / Traensyr Gate
Crossroad Caves
The Inbetween Ruins
The Scamander
Windy Canyon
Shore of the Dark Lake / Fortress Mur / Dark Lake Islands / Dark Canal / Canal Ward/ Lower Sanctuary
Underwater Areas / Parts of Dunwarren Ruins
Lowest Parts of Dunwarren Ruins
Lowerdark [i](Way, way below....)[/i]
The stairs leading from Upper to the Gate are not particularly long, the distance from Upper to In Between and then to Lower is fairly substantial (it is difficult to make out anything in Lower Sanctuary from above)