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."