Completing the above thought, WoB consists of about 30 locations. Most of the main towns are more-or-less intact in WoR. It's the "intermediate", mini-dungeon type areas that vanish in WoR. Those are precisely the areas shown in snapshot at game's finale.

As I wrote the above, I just realized for the first time that caves themselves, more generally, have a special symbolic significance in the game. Or at least, we deal with a LOT of caves throughout the game. They commonly symbolize the good guys, or something like it. The Returners hide out in a cave. The Espers themselves hide out in caves, both in their own world and in the human world. Terra and Locke navigate the Narshe cave system when they have to, which is also where Mog and Umaro live. Figaro castle has a fantastical engine configuration which lets it submerge, thus becoming an artificial cave. Sabin is found at the end of a cave system, Cyan is retrieved much later at the end of a cave system where he has gone into hiding, Gogo is found at the back of the "Zone Eater's Belly" which nevertheless looks suspiciously like a cave, Shadow/Relm is found at the back of the small Veldt cave, Locke at the back of the Phoenix Cave. Darill's Tomb is a sort of underground cave, which improbably houses the last remaining airship. Celes is initially found in a cave-like basement area. Strago and Relm both are in the party permanently, together, in the middle of the Esper cave challenge, where Strago advances the plot a bit with some exposition.

That might be reaching a bit. After all, many of these are just straightforward dungeon crawls that generally happen to be caves, with their own hazards and rewards (re-gaining party members being the best and most important reward), but these "natural" dungeons are usually less scary, and distinguished from the truly dangerous or malevolent places in the game, the man-made places: Vector in general, with the Magitek Research Facility at its heart, and later Kefka's Tower.