I really love Fit Republic - my friend and I joined last summer right after they opened. It's the first concept of its kind (they are owned by Mountainside Fitness) - strictly a studio gym. They only offer classes but they have everything from Spin to Yoga to Crossfit to Barre, even a hot yoga studio and high intensity interval training (HIIT). It's nice to have a variety. The space itself is beautiful and the employees/other Citizens are really friendly! I am partial to spin, the DJ classes are super fun! All the classes I've tried are definitely challenging and not targeted towards Beginners.
The location is nice being right in old town but parking is a serious pain especially when you are running late trying to make it to class on time. I do LOVE the fit republic app!! Makes finding a class easy and just registering right from your phone is great. Check out Fit Republic if you are looking for something new, challenging and fun!