Gil-Var-Delle is a giant ruined tree in western Grahtwood, west of Elden Root. The Worm Cult can be found here in large numbers, accompanied by their raised skeletons as well as Daedra following the destruction of the settlement at the hands of Molag Bal.
Gil-Var-Delle Wayshrine is located north of Gil-Var-Delle and south of Goldfolly. Alyxe the hag's tent is located west of the wayshrine. You can speak with Alyxe for Alchemist services, and there is a cooking fire beneath her tent.
Despite High Ordinator Danys mentioning towards the end of the quest that the Daedra are gone and only the Worm Cult is left to mop up after destroying the Dark Anchor, the dremora around the anchor point will remain after completing the quest and clearing the location.