Hurrah, it’s Open House weekend, two days when the city’s doors that are usually shut, creak open and let us have a peek inside. Although you needed to enter a ballot to get tickets for a few, very select addresses (including 10 Downing Street!), you can just walk up to most participating buildings and stroll in. Take a lift up the Gherkin, wander around the Lloyds Building, or explore The Freemasons Hall (there’s a full list here). Take advantage of the full programme of family activities at some venues; get a bird’s-eye view of the city, and create a future, crazy London skyline at City Hall, or design a pavilion of the future with real-life architects at the Serpentine Pavilion. More about Open House Junior here. Free. Across London. September 17-18 10am–5pm, tours and workshops at various times.