Willow Creek and Oasis Springs are included in The Sims 4 base game, they are NOT secret worlds. World article including List of lots is copied from including any errors existing in their website. Due to same reason I did not made an accurate Excel list of lots in each world as I did for The Sims 3 worlds.
Please DON’T ask recommendations what expansion packs to buy, this depends by each person preferences and personally I did NOT played The Sims 4 (other than when EA GAMES allowed playing base game for free for 48 hours) so my answer will be irrelevant. The Sims 4 does NOT offer additional download-able worlds or any tool for players to make custom worlds, like Create-a-World for The Sims 3. Click each world name to see list of lots and families. Here is the list of worlds shipped with The Sims 4 base game and expansion packs (19 worlds as July 2021).
