Assassin's Creed: Odyssey Fate of Atlantis begins with a mission known as The Isu Beckon. The quest sees you reach Atlantis.
The entrance to Atlantis is found on the Island of Thira. It is one of the Volcanic Islands, found in the eastern part of the world.
To reach the gates of Atlantis, you need to teleport to Gateway to the Lost City. This activates the mission.
Once you enter the Gateway to the Lost City, you'll encounter Aletheia. She will share some valuable information and unlock the entrance to the ancient world.
Climb the stairs and enter the first unlocked area - Fields of Elysium. There you'll begin your adventure.
You'll wake up on Persephone's court. She will sic you with her army - this will begin the next mission.