After completing both 'Much Ado About Snow Elves' and 'The Excavation of the Ruins of Rkund' one can encounter the ghost outside Greenwall Cave, near Fort Greenwall (north of Riften).
Walkthrough
Follow the Ghost
Follow her into the cave and swim inside the central pool. In the center there is a hole, with at the very bottom a hatch leading to the Lost Ruins. Follow here until you can see the Falmer structures, but be carefull not to fall down, because there is no way back up.
Tell Professor Marassi about Greenwall ruins
Travel back to the Explorer's guild or if he is currently with you as a follower talk to him directly. However when used as a follower he must be dismissed before Trial of Trinimac can begin.

Greenwall Cave on the map

The ghost from afar

Hatch to the Lost Ruins
Quest Stages
The Visage (DBM_Excavation03Prelude) | |
---|---|
Stage | Journal Entry |
*10* | The Snow Elf ghost who aided me in Calcelmo's quest for the Snow Elf relics has reappeared in its normal imperative way. I should follow her.
Objective : |
The ghost has shown me the way to a hidden ruin in the caves beneath Fort Greenwall! It is quite the discovery indeed. I should let Marassi know about it. The ghost was trying to indicate a passage in the wall across the spanse, which could be something important.
Objective : | |
Marassi is gathering the explorers and setting out to excavate the snow elf ruins beneath Fort Greenwall.
Objective : |
If completing the "Follow Ghost" objective is bugged. use *setstage DBM_Excavation03Prelude 10* to complete that stage, and be able to talk to Marassi.