Last Rites is a secondary quest available in Velen, involving a bit of grave hunting.
Name: Old Woman
An old woman is standing on the bridge looking over the pond north of Blackbough; she is only there at night. The old woman will ask you to put a ring on the grave of her husband Jackamar in order to stop the hauntings that she says have been plaguing her for some time.
Following contains quest spoilers. You’ve been warned
Find the grave of the old woman’s husband .
Head northwest, along the edge of the pond, until you reach an unmarked cemetery. There will be some ghouls about, dispatch them and use your Witcher Senses to find the right gravestone and place the ring on it. At this point, use Keira’s Magic Lamp to see the ghosts reunited.
Return to the old woman for a reward.
Go back to Blackbough and find Lessy’s hut. Speak to the grand-daughter of the old woman, she will have some interesting things to reveal.