The Walled Garden once was the kitchen garden of Kenwood House (it's still called the Kitchen Garden as well). Today it's a flower garden, currently showing a colourful display of late-summer flowering plants.
Tormentil is a herbaceous perennial which can be found on the acid grassland of Hampstead Heath.
Here it is growing on the slope leading down to the stream between the Vale of Health Playground and the Viaduct Pond.