The Cathedral is the first section of the dungeon beneath Tristram. It features clear human architechture, and resembles the curch underneath which it is built. The lever structure is mostly made up of large rooms connected to each other by doors, with small dead-end rooms appended on the sides througout the level. Many of these rooms feature Skill Books and Scrolls, and scouring the first four levels for useful spells can be very useful for newly started characters, sometimes even enough to warrant a restart of the game to rerun the first four levels again before tackling the Catacombs.
From underneath the Cathedral, Diablo started corrupting the town of Tristram, the capital of Khanduras. The mazes underneath the cathedral were the stage for the entire game. Entrance to the first level was accessed through the Cathedral front entrance.
Upon entering Level 1, the character mentions, "The sanctity of this place has been fouled."
Gharbad the Weak: A goat man named Gharbad begs the player not to kill him, and in return he will forge the hero a weapon. Upon finishing the weapon however, Gharbad attacks. He then drops the weapon upon his death.
Ogden's Sign: Ogden has had his sign stolen by some demons, and as it turns out a Dark One named Snotspill is behind it. He offers to return the sign if the player kills some Overlords for him. Upon finishing said task and returning to Snotspill, the monster attacks with his allies.