Isles of Dread Sandbox

Original X1: Isle of Dread cover art

ther related concept would be the idea of the adventure island. Whilst searching for the cover art of the Isle of Dread adventure module (not the original image above, the one I used in this post), I came across this post on the Hydra's Grotto. As the author rightly remarks, the Isle of the Dread represents a great potential sandbox setting. As well as the rich variety of lairs, settlements and weird encounters (cannibals! Kopru! ankylosaurs!), the island is actually much bigger than might be assumed. The real world analogy used here is Ireland, and the author notes that this demands the Isle of Dread be treated as it's own campaign setting. 

(As a side note, a fantasy Ireland during the era of St. Patrick would make a great sandbox- the mythical realm of the sidhe representing a "feywilde" that could play foil to the mundane, christianised territories).

"Adventure Island" can be somewhere the characters visit to seek their fortune, with only a rough map to guide them (the module includes a player handout depicting only the coastline) to potential treasures and mysterious locales, buoyed by the rumours of sailors and pirates. Perhaps the adventurers set up camp in the village of Tanaroa (which though exotic, is inward looking and conservative and fearful of the weirdness lurking beyond the boundaries of their territory).