One of the tablets needed to obtain Excalibur can be found in the basements of East Anglia, more precisely in the caves of Grime's Graves in Assassin's Creed Valhalla.
Go to the point of the spot and then dive into the hole to land in a haystack. The rest is simple: follow the path, always straight ahead, without ever lighting a torch. Along the way, you should even come across one of the famous totem poles of the cursed area to be blown up.
Don't hesitate to use Odin's vision to find your way through these gloomy corridors, until you arrive at a desk and a chest — containing the precious tablet needed to advance Excalibur's quest.
Original content by Bastien "Lloyd" Dubosq-Luyer.