http://www.fitnessfirst.co.uk/try-us/try-a-club/
Using the day pass you can access the gym facilities, sauna / steam room, and classes (although you won't be able to book in advance). They have Yoga, pilates, weights classes etc (you just need to check out the timetable)
(If you have no intention of joining, give them a fake mobile number and then they won't pester you, but shhhh don't tell them I told you!)
