Mine are on their own, indoors for 9-10 hours in the week. I'd love to set up a hidden camera to see what they get up to.
I hide dry food and treats around the house and most of it is gone when I get home. I also hide a few of their toys in different places. THey have two cat trees, two fat boy scratching posts, a tunnel, a tent, various boxes, two water fountains and a tree stump. When I get home the tunnel is always collapsed and the tent is either upside down or on its end. So they do a fair bit of playing but lots of sleeping. They are usually waiting at the door when I get home, for food if I'm honest!