Free session of British Military Fitness in Whitlingham Country Park, Norwich
Monday evening, Wednesday evening or Saturday morning
Described as "the UK’s biggest and best-loved outdoor fitness classes - BMF is the best way to get fitter, faster, stronger and have fun whilst doing so"
Not my cup of tea, but people who I've spoken to about it say good things.
You have to sign up in advance here
NB Whitlingham Country Park does charge for car parking, but you can park further down Whitlingham Lane on the verge for free, or cycle there (bit cheeky, but it's also cheeky to charge for car parking!)
Also available elsewhere in the UK- Classes over the UK