>>14494316
Rimworld is a lot of fun I'm playing it recently.
>>14494400
Kenshi is also a lot of fun and playing that too.
I feel like Terraria is also mostly a sandbox, though it's a side-scrolling 2d version of one.
My last suggestion doesn't belong I'm going to say Elona is a fun game where you can dick around endlessly in a no-permadeath-roguelike setting, and instead of sand you have your own exhaustive character development and that of your pets and property (castle/house/dungeon) to keep you busy between dungeon runs and quests, that you do at your own pace.