If you're looking for a challenging workout try Ten Point 5. Before coming here I had never done a barre class and it was way harder than I expected it to be, but in a good way. My muscles will literally shake during parts of the workout. It's a combination of stretching and strengthening using your own body weight as resistance as well as the barre, a ball and a strap for certain exercises. Even though you're not running or jumping or anything like that you will definitely feel like you worked out at the end.
The studio itself is very nice. It's clean, well kept and bright and airy. And you have to wear grippy socks, which is not my preference but it does keep the funk factor of the mats down I guess.
This is good alternative if you don't like regular gyms or are looking for a different kind of challenge.