Like stepping into a small slice of Victorian London, a visit to this covered mall off Gracechurch St is a minor time-travelling experience. There’s been a market on this site since the Roman era, but the architecture that survives is all cobblestones and late-19th-century ironwork; even modern restaurants and chain stores decorate their facades in period style here. The market appears as Diagon Alley in Harry Potter and the Philosopher’s Stone.