Speak with Zorus the Judicator at Wildhammer Stronghold.
The history of Shadowmoon Valley is a long and troubled one. Few delve into it for fear of breathing new life into the unspeakable atrocities that took place there.
Not all are so timid, though. Zorus the Judicator searches for the truth about the ghosts of Shadowmoon's past. It is a staggering undertaking, one with which he would welcome help, I'm sure.
If you should venture into the valley, look for Zorus at Wildhammer Stronghold, in the central portion of the valley's southern region.