A person happens upon a bag of crystals that allow her to travel. For every trip she takes, a crystal is consumed, and steals a part of her soul. If she uses all the crystals, she dies. But each place she visits is increasingly more fantastic and unbelievable, and she can’t help herself. The wanderlust is something she has to fight.

Maybe towards the end, the worlds become darker and scarier, so that she has to escape them more and more and use more crystals.