Yeah, the ruins of the castle in Castlevania II is pretty cool, especially since it's completely barren except for when you revive Dracula, so it really does feel like it was left as-is from the end of the previous game.

Although if we start to include games that only reuse a portion, then we'd have an exponentially larger pool of examples. Seems like a lot of developers like to include a little bit of a past game as fan service, but it's rare to see a representation of the entire previous game. I wish more developers were clever like the Zelda II creators. It's great when you can visit the same towns and traverse the land basically as you did before, but it doesn't have to always be done that way. The representation of the original Zelda map has almost nothing to do on it and you can walk across it in seconds, so it's not a big part of the game or something that took much effort on the part of the developers. And since it's small and abstract, the reference isn't screaming in your face. When I first encountered it in Zelda II, I felt that something was suspicious about the area, but it wasn't until I read other people pointing it out and showing the comparison that it clicked.