A great example I can think of is the "My Pet Dungeon" mode from Dungeon Keeper 2. At your own pase, without risk of attack, make the perfect dungeon within the games mechanics. No challenge? Wrong. You have to unlock the privileges with some challenges that lock certain privileges behind paywal... wait, no, doing stuff in game . I know that's mad these days.
War of the Overworld, the spiritual successor to Dungeon Keeper, also has this game mode. Buy it. Play it. But also, pay for it. It wouldn't be right if I didn't point out this feature is a paid DLC, but I swear this game is worth it.