This is from the 'Nietzsche Haus' web site:
"At the beginning of July 1881, Friedrich Nietzsche visited Sils for the first time, staying at the home of the Durisch family (today's Nietzsche Haus), where he rented a room on the first floor. From 1883 to 1888, he returned here every summer. He had found a place that gave him peace and enabled him to concentrate, a landscape which - as he said himself - was "blutsverwandt" (related by blood). Here, he worked on a number of books during his 7 summer stays (1881, 1883-88), e.g. Part 2 of "Thus Spoke Zarathustra", whose key idea of eternal recurrence came to him in a moment of inspiration on the shore of the Lake of Silvaplana."
In 'Ecce Homo,' Nietzsche wrote:
"... "this highest formula of affirmation that is at all attainable, belongs in August 1881: it was penned on a sheet with the notation underneath, '6000 feet beyond man and time.' That day I was walking through the woods along the lake of Silvaplana; at a powerful pyramidal rock not far from Surlei I stopped. It was then that this idea came to me."
Watch this video: http://www.youtube.com/watch?v=GyNYtVW9TH0