Ghouls, Grave Hags and Mourntarts. This relatively easy Contract is pretty darn grisly.
The Witcher 3: the Merry Widow Contract
Suggested level 10
You'll find this quest attached to the noticeboard in Oxenfurt, where you'll then need to travel to the Lindenvale signpost.
There's funny goings on in the cemetery, and it's your job to go investigate. At the cemetery you'll be attacked by wild dogs, attracted by the bodies dug up by Ghouls.
Use your Witcher sense on the graves and you'll follow a stench trail over a bridge to a small house. Investigate the inside and you'll discover you're looking for a Mourntart. Now take the Grave Hag's skull back to the cemetery.
Back at the chapel place the skull on the altar and the Mourntart will appear. Don't be temped to stay in the chapel as you won't have enough room to fight.
How to kill the Mourntart
Although this is a suggested level 10 contract, it's much easier than that.
Mourntarts are vulnerable to Black Blood, Necrophage Oil and Yrden and Quen signs. She uses sharp claws that can't be blocked and a very quick tongue attack.
It's easy to keep casting Quen on yourself for protection and attack quickly, making sure you don't trap yourself in the small confines of the graveyard. Once killed, loot the body for a trophy and head back to the gravedigger for 240 EXP and whatever crowns you negotiated.