We got so ma ny worlds now that I randomly run into a place that I barely recall to have sen in the past, but forgot existed. This is one example, in Mt. Komorebi: In my game I have a traveling ...
First I thought there is a lot.. but then I read your text more carefully and you mentioned visitable places.. and suddenly my mind went blank 😅 I mean there are lots of gems like this but not visitable by sims.
Here few what came to my mind.. sorry these most likely are obvious 🙃
This falls under "Mystical" , In one past save, it was a old tomb of a famous vampirehunter (who also was a werebeast) . In Forgotten Hollow.
Then... better yet if you can build there? then of course these in Windenburg... again obvious, but I havent played in Windenburg for literally years, and keep forgetting these are a thing.. Blufffs and Ruins.
Also this handy picnic spot at forest side of Wburg... Who knows maybe those ruins were once something important??