The phrase "indoor gym" refers to a place or facility that is built indoors for people to exercise and participate in physical activities. Full definition
A small indoor gym, and a tennis court, is part of the amenities of this beautiful resort. (seasidemexico.com)
Communal facilities include three outdoor swimming pools (one on the fifth - floor solarium and one a 25 - meter lane pool; see pictures), three floodlit tennis courts, poolside bar / restaurant, landscaped gardens and kids» playground, table tennis, billiards and a small indoor gym with treadmills, bike, cross-trainer & pilates / yoga floor. (rentals.holiday-home-rentals.co.uk)
The field houses, in a new network of small neighborhood parks, offered separate indoor gyms for boys and girls, English - language programs, early branches of the Chicago Public Library and public bathing facilities. (articles.chicagotribune.com)