Grotto
The Grotto is accessible from Floors 3-5. It leads to the River.
You'll find plenty of Vipers, Rats, and Eels. Even the occasional Mercenary or Grunt. The biggest danger here is finding a Crocodile.
With ample blood bags and few torches, this branch is usually easier as a vampire. However, pools of water and sunlight dot the floor and sometimes make exploration difficult.