Good questions Jimmy.

The theme of this challenge is travel hence I believe that unless you have to "travel" to that extra part of your world, it would be the same. Also it was specified that each location should have their own visual look and feel. So there should be some effort to give each location it's own distinct look visually.

How close is the desert, oasis and pyramid from each other? How much swimming (distance) do you have to do to get to the underwater shipwreck? Based on these things, it's up to the judges to determine how many actual locations you have in the game.

If for example you have to auto-travel a long way to the island from the desert then the oasis is just on the horizon and the pyramid is right beside it then I'd say that those would definitely not count as separate locations in my books, just make-up a more complex single location. The spirit of the challenge is for the teams/individuals to make 3 separate areas or locations/regions or levels in your game that players travel to/from.

I would make it feel like you are in a totally different "location" by stylising each spot you want ot be considered a location. From there it's up to the judges to tell you how many locations you ended up making from intention or not. Just be sure to make at least an obvious 3 locations or you might "fail" the actual "challenge" part.

Now as to the revisiting, it doesn't matter if there is a point to revisiting those places again, as long as you can in the same play-through. That said, if you can figure out a point to going back as well then you may score better on the innovation or fun factor score categories... There is some balance to consider in your design.