Gyms and complements to gyms (such as saunas) can be carved out of awkward space you're not sure how to use — or if you're one of the lucky few who have too much closet and not enough stuff.
I'm don't think we want a space this large dedicated to work out equipment. But, a large closet downstairs to hold the equipment with multi-use space to then use is possible. I also like the idea of a dry sauna! Sauna near workout space/downstairs instead of master suite allows for kids to use it?