Big-box gyms follow the wide avenues rather than the old centre. Gran Vía, the Eixample and Avinguda del Cid hold the chains, Extramurs and Abastos serve the dense residential blocks behind them, and CrossFit boxes sit in converted industrial units around Camins al Grau, Patraix and out towards Alboraya. Ciutat Vella and El Carmen have almost nothing, so the old centre usually means a ten-minute walk or a bike ride.
Joining is a two-part cost: a matricula paid once, then the monthly cuota taken by direct debit from a Spanish account. That account needs a NIE, so ask whether they take card payment for the first months. Check for a permanencia clause and for the cancellation rule, which normally requires written notice before a set day of the month.
Chains open early and close late on weekdays, with shorter Saturday hours and often Sunday mornings only, while coach-led boxes run fixed class slots you reserve in advance. August is the quietest month of the year and many boxes drop to a summer timetable. Front desks work mostly in Spanish, though chain apps and contracts are often available in English, and the training floor needs very little language.