Mercat de la Boqueria
Time Out says
Thronged with tourists searching for a little bit of Barcelona's gastro magic, and usually ending up with a pre-sliced quarter of overpriced pineapple, Europe's biggest food market is still an essential stop. Admire the orderly stacks of ridged Montserrat tomatoes, the wet sacks of snails and the oozing razor clams on the fish stalls. If you can't or don't want to cook it yourself, you can eat instead at several market tapas bars.
If you visit in the morning, you'll see the best produce, incluing the smallholders' fruit and vegetable stalls in the little square attached to the C/Carme side of the market, where prices tend to be lower. But if you come only to ogle, remember that this is where locals come to shop. Don't touch what you don't want to buy, ask before taking photos and watch out for vicious old ladies with ankle-destroying wheeled shopping bags.