Lately I've been thinking about how well some classic adventures might adapted to real world settings. By real world, I mean historical fantasy--I'm not thinking of throwing out magic. Some monsters or at least, their abundance might be sacrificed, though. Harryhausen fil-esque beasts would be fine; tribes of orcs or goblins would likely be reskinned.
There are, of course, a number of dungeoncrawls which could take place pretty much anywhere with a little work. Here are a few that I recall with more distinct locations:
The Sinister Secret of Saltmarsh: Given that we're told the setting of this one is meant to evoke a south-coast English town, the obvious placement for me (inspired by Captain Clegg) would be the set on the southeast coast of England in the area of Romney Marsh. Of course, that's not the only option. The Low Country would work, too. The significant presence of lizard men in the area might need to be reskinned as something else, but maybe having this have to do with Deep Ones off the coast would work?
Beyond the Crystal Cave: This one reminds me of The Tempest (though it's probably the similarity of the name Porpherio to Prospero and the island location that does that) so I would place it on Prospero's Island in the Mediterranean, which could be Pantelleria as some have suggested or a completely fictional Mediterranean isle.
Aerie of the Slave Lords: My initial thought on this one was the Barbary Pirates, but that name is usual reserve for pirates that are a bit later era than might be the sweet spot. Fortunately (in this context only!), slave trading in the Mediterranean was quite common in the Middle Ages. You don't have to go to an "evil" nation like a Pomarj, you just have to go to Venice. Some Mediterranean port could be a stand-in for Highport, and a fictional mediterranean volcanic island in the Companian volcanic arc would be the sight of the slaver's secret base.
Anyway, you get the idea.