The Last Bell is one of the Five Keys that can be combined to restore Kela the Guardian to her corporeal form. It is thought to be buried deep under ice near the South Pole.
The Last Bell is supposedly a gigantic bell that is said to have been created at the dawn of the iron age. It supposedly weighs more than 3 bull elephants. The legendary device is supposed to have fallen into an ice crevasse after destroying everything within a three mile radius of it.
The humans and their allies brought back to the Arcanum a series of earth from around the bell as well as metal shavings from the bell. The Arcanum plans to use the Last Bell as a test project for their great manhattan project, and should theoretically be able to teleport the Last Bell before trying to teleport the Sampo.
The group has left the Last Bell where it is for now, planning to summon it only when they need, because the thing is so incredibly dangerous.