Sleipnir

Sleipnir is Odin's grey eight-legged steed, the swiftest of all horses, able to gallop over sea and sky and down into the land of the dead. He is born of Loki, who, to save the gods from paying their wall-builder, turns into a mare and lures away the giant's mighty stallion Svadilfari; from that union Loki bears the foal. Odin rides Sleipnir on the road to Hel to question a dead seeress about Baldr's doom, and his son Hermod borrows the horse to leap Hel's gate and beg for Baldr's release. No barrier between worlds holds him back.