Baba Yaga is actually found in Novgorod, but as of 2025-08-23, that area hasn't been added.
To seek Baba Yaga, buy flour and mutton at The Welcoming Rusalka Inn and then head east into the forest outside of Novgorod. You may have to have detect hidden on to see her hut with chicken legs.
Give the "maiden" the flour and mutton, and she'll invite you into the home. She'll transform into a matronly woman offering to cook for you. Open the oven and she'll shove you into her lair. You'll take a few hundred damage from that.
The area contains aggressive bats that you'll need to clear out. Baba Yaga will be in several spots throughout the cave. As you attack her, she'll flee to another spot in the cave (all her hidey holes are tunnel rooms) while healing. She can cast meteor which packs a wallop.