You can stay fit without going to a gym in several ways. For instance, you can find various sport workouts on YouTube, such as High-Intensity Interval Training (HIIT), Zumba, and more, that require no gym. You can do these workouts in the space available in your flat or room.
Another option is to engage in outdoor sports. Many sport parks provide numerous training opportunities. If you don't have a car or the sport park is too far, jogging in the surrounding nature is an excellent way to stay fit.