If you live in London you’ll be used to seeing the city’s iconic buildings from the outside, but have you ever been inside the Gherkin, Heron Tower or Tower 42?

Well, if you haven't, you'll get your chance this September at Open House London. Taking place over 48 hours on 22 and 23 September, the city-wide festival will see more than 750 buildings of all kinds open their doors to the public, alongside a programme of neighbourhood walks, engineering and landscape tours, night-time openings, urban jogs and talks. And it's all free.

In celebration of the 20th annual Open House London event, the organiser, Open City, is promising that this year's festival will be the biggest and best yet, and 'a unique opportunity to see, explore and learn about London's amazing architecture and design'.

Taking 'the changing face of London' as its theme, this year's event will explore issues relevant to London's local communities and how the built environment is evolving - including the design of homes, the impact of climate change, the role of architects and contemporary design in revitalising places and, above all, how good design can make London a more liveable, vibrant and enjoyable city.

It will also explore the transformation of east London and the Lea Valley with expert-led events showcasing the regeneration of areas surrounding the Olympic Park.

Visit the website for more information.