Q:
"Down" icon in Divinity's Reach
A:
I’ve been wondering about this since beta. There used to be an “Up” marker inside the Great Collapse, where the scaffolding is (behind the gate with the Royal Architect in front). Back then, I assumed the two were somehow connected, but one has disappeared since.
Someone on the DR Wiki page said the following (spoiler?): “it’s the entrance to the crypts that Ghosts of Ascalon starts in”
Those crypts will likely become playable at some point in the future, possibly as a full-blown dungeon. That may well be the entrance.