Yes! With OneFit you can not only follow group lessons but also train in the gym. You are free to use the fitness equipment at all OneFit gyms - just check the opening times in the description. You can search through your local gyms by using the 'Gyms' filter.
If you decide to use the gym at a venue you still need to check-in. This can be done by opening the app and clicking on the 'Check In' tab at the bottom of the main menu. After the venue is found on the map, the option to 'Check In' will appear. Click 'Check In' and then confirm your check-in. You will then see your check-in confirmation screen.