If I were you I'd look around at different gyms or physical activities until you find something you enjoy. There are tons of different options (to name a few: yoga, climbing, mountain biking, swimming, power lifting, running, that thing I sometimes see on TV where you competitively try to chop wood faster than other people, etc...). Try a bunch of stuff out and I bet you'll find something you enjoy going to more than the type of gym you described. Many also have mental aspects, while not a replacement for keeping yourself more generally cognitively engaged probably help with that to some degree as well