The government that oversees the Square Mile of the oldest part of London gives written and performance-based exams to the experts who lead its excellent weekly tours. The experience is less theatrical and denser with facts than what London Walks (see below) generally provides, and group sizes tend to be smaller, too. There are 18 from which to choose (from thrice weekly to monthly), including ones on Dickens, the City’s top 10 sights, and Roman London. Tours are 1 1/2 to 2 hours. Pre-booking is advised, but not essential.