In the summer this is a haven in the middle of the city. It is a public garden where I like to go and relax in the grass under a blooming tree. There is also a cafe and a shop here. Before you leave you should buy a bouqee of flowers (you pick yourself in the garden!).
A 500-meter long (quarter mile) walking path with a magnificent view of Lake Mälaren, City Hall, and Riddarholmen. Bring your take-away coffee and walk the path at least once every season to notice the different scents and colours of Stockholm.