BTW, Congratulations? Is this your Honeymoon cruise?
Your question is a great one. You will find on Celebrity ships, a dedicated staff with state of the art equipment devoted to spa and fitness. What I enjoy about Celebrity's fitness center is primarily the view (overlooking the ocean) while working out. The panoramic floor to ceiling views are cool, bu the equipment is (generally) the latest in weight-training and aerobic. There are many specialized classes as well as personlized trainers to assist with your regime or goal.
The spa area is wonderful after a workout as well...hydrotherapy, steam / dry saunas and a full line of individual or couple's spa services (four hands massage, etc.).