Lore
Positioned next to Heide's Tower of Flame, the cathedral is one of the few structures to have survived whatever cataclysmic event submerged the surrounding area and the subsequent centuries of erosion by the wind and waves.
The Old Dragonslayer waits inside the cathedral to challenge anyone foolish enough to enter. It appears that we still haven't seen the last of Lord Gwyn's mighty knights - Dragonslayer Ornstein appears before us once more. But this time, he's alone, and something seems… odd. Instead of the lightning powers that he once possessed, he attacks with the power of Darkness. Is this truly the same proud knight we faced in Lordran so long ago? If so, the flow of time is distorted, indeed. If not, then where else could this Old Dragonslayer have come from?
After slaying him, Blue Sentinel Targray, the original leader of the Blue Sentinels covenant, can be found on a balcony overlooking the sea.
The cathedral was likely built to worship Flann, the god of flame. Thus, the Old Dragonslayer is probably Dragonslayer Ornstein, the protector of Princess Gwynevere, who ran away with Flann.
Connections
Theories
The Statues Inside
NEXT: Cave of the Dead