If you want to have a view over hole London, you definitely have to go to the Sky Garden. The Bar/Restaurant in the 35th floor offers a 360-degree view over the city.
The 20 Fenchurch Street which nickname is “Walkie-Talkie” because of its shape, has been built in 2014. The skyscraper was designed by the architect Rafael Vinoly and costs about £200 million. Except of the Bar, the remaining floors are built for offices.
The Sky Garden was opened in January 2015 and is free for public since then. But if you want to be sure to be allowed to go up, book a ticket online in advance. Then on busy days, only people with tickets can go up to avoid an overcrowded place. Click here to book your private ticket.