The Whispering Hillock
Side quest
Velen suggested level 5 
On the world map
From the journal
Something about life in dreary backwoods settlements leads their inhabitants to hide the truth with misleading names. This takes the form of both hyperbole - a clump of bare trees called "Dragon Spike Forest" or a hole in the ground two paces deep named "The Chasm of Eternity" - and understatement - a horrid massacre calmly referred to as "the incident." Velen fit the mold in this regard, as Geralt learned while he wandered through it in search of Ciri. There he encountered a trio of highly suspicious magical sisters called the Ladies of the Wood, who directed him to a clump of bogside huts known as Downwarren. Geralt was to solve their "problem": a rash of mysterious murders. He spoke to the ealdorman and learned that the evil power behind the killings dwelled in the Whispering Hillock. Wherever else?
The truth hidden under the Whispering Hillock? A woman's spirit, imprisoned in a cave within it. Geralt felt sympathy for the ill-treated ghost and helped it enter the body of a horse, thus regaining its freedom.
Depending on the outcome: … A woman's spirit, imprisoned in a cave within it. Geralt concluded this foul being was responsible for murdering the inhabitants of Downwarren, and so destroyed its heart, loosening its last grasp on our world.
While roaming the thick, gloomy tangles of the Velen woodlands, Geralt came across a spirit whose heart was trapped in a cave under an eye-catching tree…
