1) The Natural History Museum
Discover the secrets of the deep sea, explore coral reefs and meet the dinosaurs at the renowned Natural History Museum. The Blue Zone introduces you to dinosaurs and giant mammals, with a gallery of fascinating nature photography. The Red Zone takes you through a giant earth sculpture, where you can learn about the power of volcanoes and earthquakes. The Green Zone explores the wonders of evolution, and in the Orange Zone, you can see scientists hard at work, and visit the wildlife garden.
There are 35 rooms of incredible exhibits, with the most intact Stegosaurus fossil skeleton in the world (in the Red Zone). There are regular free talks, tours and events for families.
Insider Tip: Download the Museum app to help you make the most of your trip.
Nearest tube station: South Kensington
Cromwell Rd, London SW7 5BD, 020 7942 5000, www.nhm.ac.uk 

2) Camden Market
Camden Lock Market Hall photo by Steve Haslam Wikimedia Commons
Camden Market is a vibrant, buzzing melting pot. This is a place where you can buy a holographic circuit print corset, or an exquisitely tooled bespoke leather bag; a necklace from Egypt or a doll from the 1930s. Where you can sip organic coconut tea, or sample over 100 varieties of rum; where the cuisine options are endless, from octopus to burgers, from Malaysian to Ethiopan, from mac and cheese to sushi in a bun.
Insider Tip: Every Thursday, 6pm to 10pm, the Camden Night Markets will be running, with free music and a fantastic atmosphere. 
Nearest tube station: Camden Town
56-56 Camden Lock Place, London NW1 8AF, 020 3763 9999, http://www.camdenmarket.com

3) Portobello Road Market
Portobello Market is a charming, vibrant, eclectic space, beloved by Vogue columnists, bargain hunters and antique dealers. You can see the racks of vintage clothes which inspire contemporary designers, or explore history in the form of antique lace, retro 1950s kitsch and 1960s tailoring. Experience other cultures, with French soap, Russian scarves, South American jewellery and fair trade handbags. Most of the antique dealers are there on Saturdays, but prices tend to be cheaper on Fridays.
Insider Tip: Get there around 10am to skip the crowds, take a camera, and refuel at the Electric.
Nearest tube station: Ladbroke Grove or Notting Hill Gate
Portobello Road, W10 5TA, 020 7727 7684, http://shopportobello.co.uk/

4) The Science Museum
With over 15,000 objects on display and an exciting range of interactive exhibits, the Science Museum is fun, free, and fantastic. It’s perfect for kids (and big kids) who love robots and making things with their hands. You’ll meet robots who can write, and Adam, a robot who can carry out scientific experiments. Younger children will love the interactive storytelling events, and for older kids there are plenty of fun, free workshops. You can make a colourful magic lantern, a pop up Science Museum, an artistic doodling machine and your very own hand-made rocket mouse!
Insider Tip:  Open until 7pm during school holidays (last entry 6.15pm) so consider popping by later!
Nearest tube station: South Kensington
Exhibition Road, South Kensington, SW7 2DD, 020 7942 4000  http://www.sciencemuseum.org.uk

5) Portobello Film Festival (4 – 20th Sept)
Dubbed ‘the wild side of Brit Film’ by the Metro, Portobello Film Festival divides into three sections; pop up cinemas, The Muse, and 50Golborne. This free festival spans a wide variety of venues, incorporating open air screenings, plush theatres, clubs and bars.  Their remit is to highlight new and exciting ventures in British film, from showcasing cutting edge film makers (it has seen the debut of directors such as Guy Ritchie) to highlighting new media formats.
Insider Tip: Don’t miss Fuseli – the short film about cats, night terrors and sleep paralysis
Nearest tube station: Ladbroke Grove or Notting Hill Gate
Unit 11 Acava, 54 Blechynden Street London W10 6RJ, http://www.portobellofilmfestival.com

6) Tate Sensorium 
The Tate Sensorium is a feast for all the senses at the Tate Britain. It comprises four paintings from the Tate Collection, with sounds, smells, tastes and physical forms inspired by the artwork, for an almost synaesthetic experience. A 3D acoustic experience is created with ‘ultraphatics’; projected soundwaves that create sensation if your hand moves through them. Master chocolatier Paul Young, scent expert Odette Toilette and audio expert Nick Ryan have been drafted in to create the project.This intense, sensual exhibition is a free 15 minute experience, with tickets available on a first come, first serve basis.
Insider Tip: The truffles available with Francis Bacon’s work reflect the nature of the piece; edible charcoal, smoke and flowers.
Nearest tube station: Pimlico
Millbank, London, SW1P 4RG, 020 7887 8888, http://www.tate.org.uk/whats-on/tate-britain/display/ik-prize-2015-tate-sensorium

7) The Sky Garden
The Sky Garden is at 20 Fenchurch Street, ensconced within a glass dome and home to three floors of public gardens, restaurants and observation decks. The highest gardens in London offer stunning 360 degree views of the city. The gorgeous grounds are planted with species designed to flourish in the light under the dome; water efficient, drought resistant plants from the Mediterranean and Africa.
Insider Tip: Entry is free, but you have to book, and have just an hour from your time of entry. Use it wisely!
Nearest tube station: Monument
20 Fenchurch Street, London EC3M 3BY, 0333 772 0020, http://www.skygarden.london

8) Kenwood House
Kenwood House is nestled on the edge of Hampstead Heath, set within tranquil landscaped gardens and an ancient woodland. The breathtaking art collection is home to classics ranging from the pastoral work of Vermeer to the fevered brilliance of Turner. The grounds are graced by the exquisite abstract sculptures of Barbara Hepworth, and inside, you can learn the true tale of Dido Belle, who helped end slavery in the United Kingdom.
Kids will love the explorer backpacks, and every last Sunday of the month there are interactive storytelling sessions for families; there is also a buggy park, and baby slings available to borrow.
Insider Tip: Get more from your excursion with their new free App which helps you discover more about the house, the collections and amazing stories.
Nearest tube station: Highgate
Kenwood House, Hampstead Lane, Hampstead, NW3 7JR, 020 8348 1286, http://www.english-heritage.org.uk/visit/places/kenwood/ 

9) Notting Hill Carnival (29 Aug – 31st Aug)
An explosion of music and colour, the Notting Hill Carnival bursts onto the scene during the August bank holiday. The festival kicks off at Emslie Horniman Pleasance Park and generally attracts over 1 million people to the Kensington and Chelsea borough. The fabulous floats, colourful parades of costumed dancers, the calypso music, the delicious Carribbean food… it’s a feast for all the senses.
Insider Tip: Try the jerk chicken, and wear your dancing shoes!
Nearest tube station: Notting Hill Gate, Latimer Road or Royal Oak
Notting Hill Carnival, Hampstead Lane, Hampstead, NW3 7JR, 020 8348 1286, http://www.thenottinghillcarnival.com/

10) Free Royal Walking Tour, Changing of the Guard
This two hour Golden Tours free Royal Walking Tour follows the footsteps of Britain’s monarchy. Learn about Kate and Will’s fairytale romance, see where the Queen buys her perfume, see Westminster Abbey and other key attractions such as Garrad’s Jewellers, the Ritz hotel, and St James’ Palace. You will either see the changing of the guard, or the Horse Guards, depending on availability.
Insider Tip: The Changing of the Guard at Buckingham Palace is a definite highlight.
Nearest tube station: Victoria or Green Park
Golden Tours Visitor Centre – Leicester Square, http://www.goldentours.com/the-royal-walking-tour-changing-of-the-guard

Get the full guide here: 50 Free Things to do in London