Starting at Swiss Court, Swiss Ct, London, UK, open the Explorial app and enter the 6-digit game code that you received by text and Viator chat message. The riddles take you from Leicester Square through some of London's most storied streets. Your first stop is Cecil Court, a narrow pedestrian alley lined with antiquarian bookshops, print dealers, and map sellers that has been trading since the 18th century and provided inspiration for J.K. Rowling's Diagon Alley. From there the app takes you to Trafalgar Square, the national gathering place at London's symbolic centre, where Nelson's Column, the National Gallery, and a pair of large bronze lions frame one of the most recognisable public spaces in the world. The route then leads to Cleopatra's Needle on the Victoria Embankment — a 3,500-year-old Egyptian obelisk that arrived in London in 1878, pre-dating the Trafalgar Square lions, the Houses of Parliament, and most of the city that surrounds it. Around 2 hours on foot through mostly flat central London. The Strand and the Embankment are pleasant whatever the season.