While finding the Sanctum of the Architect during the story of Last Epoch shouldn't take long, it can be a challenge in the post-story. Eventually, the game will take you there as part of a quest to kill Architect Liath, but you will later leave the place, forgetting its existence for many hours. And since Sanctum of the Architect does not have a fast travel point, it will be much more difficult for you to find this place on the map and reach it.