Undead Parish is full of tough enemies. You’ll face a Fang Boar, a Black Knight, several Baldur Knights, a Channeler, and a Berenike Knight along with a bunch of various Hollows. And there are two bosses. It’s also a great way to test (and hone) your fighting abilities. Once you get comfortable fighting (and learn the layout of the area), you can use the Undead Parish as a loop where you can earn a couple thousand souls in just a few minutes
There’s one bonfire in the area, situated conveniently directly above the blacksmith Andre of Astora. There are several useful items in the area (souls and weapons, mostly), but the most important to pick up is the Firekeeper’s Soul which you can give to the Ash Maiden in Firelink Shrine to expand your Estus Flask.
You’ll find paths here that lead to Sen’s Fortress and Darkroot Garden. There’s also an extremely useful shortcut that leads back down to Firelink Shrine. Most importantly, though, you’ll find the first of the Bells of Awakening on the roof of the Parish.