This is a picture of Kenilworth Castle in Warwickshire, which was taken approximately 60 years ago.
The slide was in a series of pictures in an old wooden box and I'm not sure if the subject is just the castle, or the woman sitting in front of the castle on the grass. There were a lot of pictures of a young woman in the slide box, and I think this picture may be the same girl.
This was originally a Challenge which was won by Bruce, see the comments below.