Isle of Lost Magic
Far off the coast of the Faerunian supercontinent lies an island that cannot be found. It is not on any map, and no-one save the gods know of its existence. The Isla Magicka naturally radiates magical energy and is cloaked in a fog of misdirection, causing ships that get close enough to somehow steer around it.
Fate has conspired to allow this island to be the center of a world-shaking invasion by other-worldly entities. A series of prophecies made 1500 years ago when the island was first discovered and settled by accident tells a tale of a ship that runs aground carrying the Chosen Few who can fight this terrible threat.
The Isle of Lost Magic campaign is designed to take characters from 1st level to at least 20th level, and possibly beyond. It will work with characters of any class, though balanced parties are apt to have a slightly easier time with it. The campaign is written for a large party (5-8 players) but can be adjusted to compensate for lower party numbers by following the rules in the DMG.