A list of Gyms and Health Clubs you can visit for free, if you join one in the USA and few internationally.
---- As best I understand, if you are paying fees to a gym or health club that is a member of this organization, you can:
Walk in an work out for free by presenting your card.
IPFA International Physical Fitness Association Inc
"Provide --- members with "world wide" transfer privileges by joining the international physical fitness association, the world's largest and oldest established reciprocal association for over 40 years."
The gym here cost 20 USD per month on a two year contract. That is 480, or maybe 310 if paid in one payment. If I used 15 times per month, it may be worth it, but still calculating.