The Floating Tower from Atlantis

An entry in the Tenfootpole Wavestone Keep contest!

From the publishers blurb:

When Atlantis began to sink, the wizard Oulvert invoked powerful magics to teleport his tower to a place of safety elsewhere on Earth. However, inaccuracies in the spellcasting combined with the destructive energies of the cataclysm resulted in an unforeseeable conjuncture. The three topmost levels of the tower were swept away on the tides of Chaos, and Oulvert found his home floating on the desolate seas of another dimension. As the years went by, the hands of Fate continued to pluck the tower from one world and deposit it in another, always placing it on a large body of water far from land.

Now Oulvert’s tower has appeared in your campaign world...