Trying to recall but I believe it's the town south from where you start the side chapter. (beside the ocean) Has like 2 tile spaces of town on the world map, you can't crush it and when you interact with it, it just says WIP.
Ah, yeah, I know which one you're talking about. That's a glitch. You're supposed to be able to enter it.
You can enter it by going through the maps (not the overworld) and the progressing to the beach. But yeah, I need to fix that bug! Thanks for bringing it to my attention!