Public, no, but in general every Walmart / Starbucks / ... (except Subway) have a restroom available.

Try finding a place in Belgium... if you find one, you have to pay, even if you area already a paying customer (e.g. Kinepolis, a large theater chain) or when you're in a park there's a restroom with a friggin' card reader to charge you half a Euro to take a piss. I found a tree close-by.

And grocery chains aren't even legally required to have a restroom available to customers.