Grymforge has an elevator up to the surface that takes you to moonrise/the land near moonrise.
You get warned that exiting through that elevator you will encouter the fog-thingy - so I think it is safe to assume that it will lead to the same area as does the land exit from the main map. True Soul N says that to go up you need the lanter held by what seems the same guy Minthara sends you to meet if you help her.
Gith Creche is to be located on path to Moonrise, which is the fog location. It seems to me that no matter if you ally with goblins or go through the underdark you will still end up in path to moonrise tower => moonrise tower.
Going by D:OS2 structure in/after moonrise tower we will learn what the story is really about, spare companions get axed (speculative), we will leave current area well and truly behind and act 2 will begin (speculative: act2 - Baldur's gate, act3 - hell?).
