The main thing you need to know is that coffeeshops in Spain operate on the principle of private clubs. But especially "steam" is not worth it!
The promoters of these clubs operate in the busiest streets of Barcelona, offering memberships to clubs. The usual cost is from 15 to 20 euros, but in a competitive environment, various promotions and discounts may apply.
After paying for a membership, be prepared to follow a "specially trained person" through dark back streets and knock on small, inconspicuous doors - Barcelona coffee shops work without unnecessary noise and dust.