I have a crawling 12 month old and we go to the local library which has a huge kids section with a few toys and he just loves crawling around and pulling books off shelves, so I follow him around and replace them lol. We spent an hour and a half there yesterday and he didn't get bored and got upset when we had to go. We made two new friends too since other parents have the same idea.
Local to us is also a kids cafe with a play area at the back, so we go there and I get a coffee and he crawls around and puts toys in his mouth lol. He also makes friends here.
I invite baby-enthusiastic friends or family over because they can get excited and play with him and it's interesting for him to interact with someone new and I get a break from thinking of things to do.
I go to normal cafes for lunch and share my lunch with him and it's a new environment for him and different food to what I make so he finds it interesting even though he can't crawl around.
I do activities from parenting Instagram accounts with mixed success lol. So I put posters paints in big sandwich bags and tape it to the floor for him to squish around, or I stick coloured pipe cleaners in a sieve for him to pull out, or I put melty buttons into ice tray grooves and cover with post-it notes for him to peel off etc etc. I tell myself it's for enrichment or skills development but its mostly to pass the time. Socks in amazon boxes to open and pull out is another one. Smelling spices and herbs from the kitchen.
Indoor classes, I use Happity to find them and try to go to a few a week. Hartbeeps and the like. Baby swimming you can do without a class if you're confident. If not and you're really stuck have a splashy bath haha.
Stick him in the Pram and go to the supermarket lol.