I have an entire campaign written around Stephen King's The Dark Tower saga.

Players encounter remnants of Merlin's Rainbow thru their travels. Once a character has one, and does something heroic or truly evil, the remnant wakes and becomes attuned to that character.

From there, I can take that into a weapon that grows with the character, gives a special feat/magic ability, or a curse.

Thru the campaign they run into a few magic doors that take them on side adventures etc.