Fitness clubs and big chains
Chains and macro-clubs sell variety: machine floors, indoor cycling, directed classes morning to night and often a pool. They are the rational choice if your routine changes week to week.
Visit at the hour you will train
The gym on a Tuesday at seven in the evening and on a Saturday at eleven are two different businesses. Go at your real training hour and look at machine queues and space per member.
The contract, line by line
Check minimum terms, cancellation notice, what happens if you move cities and the fine print on joining fees. Spanish consumer rules protect against abusive lock-ins: if a clause is unclear, ask before signing.
Municipal centers as the alternative
The municipal sports centers have weights, classes and pools at district rates often below the chains. It takes some enrollment paperwork and the timetables are less flexible.