This hugely popular, capital-wide annual festival of architecture celebrates its twenty-third anniversary in 2015 and takes place over the weekend of September 19 and 20. The festival allows access to hundreds of buildings not normally open to the public – private homes, government buildings, historic sites, educational establishments and many others. Last year, new additions to the lineup included The Leadenhall Building (aka The Cheesegrater), an eco-home in Ealing and Ott's Yard, an architecturally impressive group of re-purposed sheds in Tufnell Park. 2015's buildings and series of events will be available from mid-August. Of the more than 800 venues involved, the vast majority will be open to all on a walk-up basis, but around ten per cent will require advance booking; for details of how to book see www.openhouselondon.org.uk.