Thanks. I figured it out, it actually meant living room, where Kolka is sleeping. No idea, why they're calling it a gympp1 IIRC:
1. "gym" can be translated as "спортивный зал";
2. "зал" can also be translated as "hall";
3. basically, "go to the gym" is a mistranslation, because it actually refers to the "hall[way]" at home;