What about the ocean/islands?
Find V-13;
You are given a job to locate V-13. Tandi (?) wants to find it for "historic" reasons. She only knows it's due west of NCR.
Grid by grid, you search; Eventually you'll land upon a strange encounter; A cave with some odd trash, a vault flask, a body, a holotape of the Vault Dweller's journeys, and Vic's radio. Going into the cave you find ants and rats.
To complete the quest you have to at least TRY to open the door, sonce you MIGHT find the fake vault (you can sell thus info to that guy in the bazaar, since "Maybe some gullible tribal trash might be interested.").
The site disappears once you leave.