This is the rooftop of 20 Fenchurch St (aka The Walkie Talkie) in the City of London. To get there take the tube to Bank Station and then it's just a short walk.
Photo Spot Details
To get to the rooftop you need to book in advance (google London Skygarden) but it’s free. You can’t take tripods up, but other than that you can pretty much do what you like.
The garden offers 360 degree view of central London. In this picture you can see 3 of the most famous buildings in London: Tower 42, The Cheesegrater and The Gherkin