Curbed has a fantastic feature on the problem of old bowling balls. They're discarded on a daily basis—one NYC recycler receives 3-4 each day—and being made of thermoset plastic, they can't easily be melted and are thus considered unrecyclable. Breaking them up for use in asphalt is possible, but too expensive. And I didn't know this, but bowling professionals use "reactive" balls designed to absorb oil from the lane surface to improve their performance. These balls become saturated with oil and go "bad" quickly—pros can go through up to 200 balls a year!
Is there any practical use you can think of for them? I might be able to use them for landscaping—if they weren't spherical and predisposed to roll away from the mulch beds I'd like to encircle with them. I'd also love to see what happens when I unexpectedly run over a bowling ball with the mower.
Or maybe we could paint them cartographically, turning them into globes to donate to schools. Ah, that might be a hard sell: "Free globes. They each weigh between 6 and 16 pounds, have three holes in them, and are too small for children to read."
Maybe there's a way to bond handles to them, to turn them into kettlebells?