Over the Summer we did a fair bit of T'ai Chi here at Buccleuch Gardens:

In future there may be some Sunday sessions with Mark here, and when I am in Richmond, this is where I do 121s. In the Summer it's gorgeous, the river flows by within 30m. Wrapping up warm is a good idea in cold weather, but it is well covered, and there is a fab cafe (Hollyhocks) a 1 minute sprint away. More about the gardens here.  You can see the bustop in the first picture, 'Nightingale Lane' bus route 65, or a 10 min walk from Richmond Tube and Rail Station.