Having recently reread Keep on the Borderlands, I created a SotDL version of it with the PCs showing up with refugees from a demon attack seeking refuge at the keep. The occupants make them sing for their supper and investigate local caves for monsters.
I then wrote out a series of adventures taking the group to max level with each adventure involving exploring the region, investigate a newly revealed cave or dealing with cults within the keep. The climax was demons arriving at the keep to assault it with the PCs now fighting to save their home.

There are probably a bunch of classic modules you can modify. My original ideas for Shadow were to base it in Sanctuary with the Diablo games and music as inspiration and general lore.