Fitness Club (Cologne)

Hello everybody. I am going to join a fitness club in Cologne. When I asked about the price, they said that I can choose the 21 month agreement, and if I leave the country before 21 months,I will not have to pay for the whole period but till the month I will be staying here in Germany. Is how it works? No penalty, no fees If i leave before?
Then do you have any particular fitness club in the city centre to recommend?
Thank you for your kind advice!