Starting at 1 Balloon St, Manchester M4 4BE, 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 through a city that has been at the centre of things — for better and worse — since the Industrial Revolution. Your first stop is the National Football Museum, housed in the striking Urbis building in the Northern Quarter, where the global story of the world's most popular sport is told through objects, film, and interactive displays spanning football's Victorian origins to the present day. From there the app guides you to Chetham's Library, founded in 1653 and the oldest free public reference library in the English-speaking world, where Karl Marx and Friedrich Engels famously researched Das Kapital — in a reading alcove you can still sit at today. The route then takes you to St Mary's RC Church — the Hidden Gem — a neoclassical church tucked behind the commercial streets of the city centre, its interior lavishly decorated with Victorian mosaics, paintings, and sculpture. Around 2 hours on foot. Manchester's city centre is compact and very walkable.