A D&D campaign where you start at Fine size (3-5" tall) in a teeny village where everyone strenuously avoids all experience. When your party inadvertently slays a monster, you all get to second level... and go up a size category. Now you're Diminutive (2x as tall, 8x as heavy), and are exiled from the village. You must travel the world for a cure that will shrink you back to normal, but every time you gain a level, you also double your dimensions.

It's A Small World After All.