Funs things to do with base game alone?

I played happily since the beginning just adding in packs as they came... but I had fun for a very long time with base game stuff only (before they added in all the free stuff.. which must make it nicer). Mostly I did the suggestions already talked about here. Lots of getting to know the game... making super sims and super kids/teens. Getting through every career. Trying sims with every trait. Making super kids and trying to remember to save them to my library to make "base" sims later. I absolutely loved gardening and rags to riches kind of play. Another thing I did as a more deviant player was try to make every ghost available in the game ... I got to practice my kill them off techniques and planning that way.

I like to recommend this challenge because it's pretty easy and doesn't require too much commitment. It also let's you see your sims in a different light. Basically it's a trade off play between 2 opposite or conflicting trait sims that you play until they finish a few goals. You only get to play one sim in the household for a week before switching to the other. It's fun to see what they will or will not do on their own, what trouble they might get into... and then later as you give them more skills and direction how that might influence them when you don't play them.
https://forums.thesims.com/en_US/discussion/955171/trade-off-ts4-game-play-challenge-by-eqcreations/p1