Belsize health has provided me with some amazing experiences in various therapies. I have been visiting them since roughly 2006 and it is because of such a positive outcome with one of their hypnotherapists that I took it up for myself (he sadly no longer works there).
Their osteopath sorted out a back pain in literally one session, and their massages have always provided comfort, depending on what your needs are they always recommend the appropriate masseuse.
This is one of those places that you can walk into and always find a treatment that will help you out as they offer so much.
Though the facilities and ambience are quite plain and simple, I can see that this is because they put all their energy into the great quality of therapists and treatments.