Although not the specific seven seas of Medieval folklore, the ones that probably led to the expression "sailing the seven seas," it so happens that the International Hydrographic Organization, which has global responsibility for recognizing the names of bodies of water, recognizes seven "sub-seas" within the Mediterranean Sea. These are the Alboran Sea, the Balearic Sea, the Adriatic Sea, the Tyrrhenian Sea, the Aegean Sea, the Ligurian Sea and the Ionian Sea.
I bring this up because, as I'm working on the map of my campaign setting, JOSHUA-world (not its real name), I decided long ago that the main geological feature that would dominate the part of the world that I'm mapping is a major sea called the Mezzovian Sea, which is also meant to be not unlike the Mediterranean. My "final" draft on the posterboard has enough definition and detail to really start splitting it into subseas, and I bring this up because... well, because I'm now getting to go to town assigning new names to new features. Fun, huh?
I also decided, kinda on a whim, that my Mediterranean Sea analog will be in the southern hemisphere of its planet. So, as you go north, rather than getting colder, it gets warmer. I expect the very upper reaches of my map will be the 15th, while the lower reaches of my map will be right around the 45th parallel.
This makes the entirety of my map similar to the Meditteranean region, again. The Mediterranean is interesting compared to other lands at the same parallel, because of the moderating influence of the large bodies of water and warm currents in the Atlantic. Drawing these lines across the surface of our own earth, we find that Casablanca is on a line with Little Rock; Monaco is on a line with Boston. But using an Old World analog of weather, you can think of my world as stretching from the Sahel in Africa on one hand, and a line cutting through southern France, northern Italy, Romania and the northern reaches of the Black Sea on the other. Except, as I said, flipped upside down.
I think there's some value in relating fantasy settings to the real world, at least tenuously. Unlike in science fiction, where exploring "what if?" is a key tenet of the genre, fantasy stories explore other themes, and settings that are too outre tend to defeat the purpose. Granted, I consider myself more a fan of the "weird tale" where science fiction, fantasy and even horror hadn't yet crystalized as separate genres, but conventions of all three could appear willy-nilly in the same piece of work, but still--I want elements of my setting to serve as shorthand. Spending time doing ethnographies and detailed geographic studies just to figure out how things work: that's not fun.
Speaking of fun, and speaking of the seven seas, as I was earlier, here's a video from O.M.D. circa 1991. Fun!