The Hefin Cathedral is a massive cathedral in the Hefin Clan district in the north-west part of Prifddinas off the northern path. Inside the cathedral reside Hefin monks, who sell cleansing crystals in the shop. These cleansing crystals can be used on the Corrupted Seren Stone. The Cathedral also has an altar devoted to Seren.
The roof of the cathedral is a part of the Hefin Agility Course.
As part of The Light Within quest, the Corrupted Seren Stone is revealed to be the Seren shard of wisdom. During the quest, Lady Hefin, the two Hefin monks, and the adventurer cleanse this shard so it can be used to restore Seren.