Tuonela, the Finnish underworld, is an island surrounded by the Tuonela river. It’s ruled by Tuoni (Death), Tuonetar (Goddess of Death), Tuonen tytti (Daughter of Death) and Tuonen poika (Son of Death).
Read about the Finnish gods and goddesses of death in The Finnish Book of the Dead: Gods, Spirits and Creatures of the Underworld in Finnish Mythology and Folklore by Tiina Porthan and Tero Porthan, the first ever illustrated guide to Tuonela, the Finnish land of the dead.
Finnish Mythology Illustrated 