Cape Cod/Martha's Vineyard area with a side quest (or part of the main quest) where you have to dive to several shipwrecks all the while having to evade mutant seals and Ghoul Great Whites!!!
THIS!!!!
C'mon Beth. Cape Cod is only 60 miles from Boston. And the Vineyard a 40 minute boat ride. Do. It.
edit: It'd also be hilarious if there were a JFK worshiping cult on the Cape.