There is a massive restaurant downstairs but all the fun is at the bar. Order a small cider or even better, a big green bottle of cider and get them to pour it the traditional way (there's also a funny little device they can attach to the bottle so you can pour it yourself). Each drink comes with a snack of either some chorizo or some deliciously strong blue cheese. The menu has some great-looking options and I had the bean stew with chorizo and morcilla.
The place is so authentic and I was the only non-Spaniard there. I loved it! Recommended.