Leadenhall Market

Where it sits. Leadenhall Market hides in the middle of the City of London, entered through an arch on Gracechurch Street and reached from Lime Street, Whittington Avenue and a scatter of alleys. Glass towers surround it on every side: the Leadenhall Building, the Lloyd's of London building by Richard Rogers with its services on the outside, and 30 St Mary Axe. Step through the arch and the noise drops away into a cobbled cross of covered avenues painted cream, maroon and green.

The story behind it. The ground under the cobbles is the most historically loaded in the City. This was the centre of Roman Londinium: the forum and its basilica stood here from the late first century, the basilica being the largest building of its kind north of the Alps, and fragments of its masonry survive in cellars nearby. The medieval market took its name from a lead-roofed mansion on the site, and by the fourteenth century poulterers and cheesemongers traded here under the authority of the City Corporation. The market was rebuilt in stone after the Great Fire of 1666 and again, definitively, in 1881, when Sir Horace Jones — the City architect responsible for Billingsgate, Smithfield and the towers of Tower Bridge — roofed the lanes in wrought iron and glass. What survives is one of the most complete Victorian market halls in Britain, Grade II* listed, with dragons and griffins holding City shields on the ironwork and a painted vaulted ceiling that repays looking up.

On screen. Leadenhall played the approach to Diagon Alley in Harry Potter and the Philosopher's Stone. Hagrid leads Harry through the covered avenues to the Leaky Cauldron, and the pub's blue-painted door is not a pub at all: the production dressed the frontage of an optician's shop in Bull's Head Passage, the narrow arm of the market on the north-east side, and painted its door and surround a deep blue. That door is still there and still belongs to an optician, which is the single most photographed shopfront in the City. Everything beyond it is studio work. The interior of the Leaky Cauldron, the courtyard where Hagrid taps the bricks, and Diagon Alley itself were built as sets at Leavesden in Hertfordshire, and the alley you see on screen is nearly 20 miles from the market. In Prisoner of Azkaban the pub was moved altogether, to a shopfront at Borough Market, because Alfonso Cuarón's triple-decker Knight Bus could not be driven into a covered Victorian arcade.

What you actually see today. The market's plan is a cross, with a domed crossing at the centre where the four avenues meet. The shops are a mixture of old trades and City service businesses: a cheesemonger, a long-established butcher, a wine merchant, cafés, a couple of pubs including the Lamb Tavern, which has been trading here since 1780 and has a Victorian tiled staircase worth going in for. The cobbles are original setts, uneven enough to matter if you are pushing a buggy or a wheelchair. Look for the painted ceiling bosses, the dragons on the ironwork, and the sign for Bull's Head Passage, which is easy to walk past because it is barely two metres wide.

Getting there and timing. Monument, Bank and Aldgate Underground stations are each about five minutes away; Liverpool Street is ten. The market is publicly accessible around the clock as a set of streets, but it is a working City market, which means the shops and bars open roughly Monday to Friday and the place is close to deserted at weekends. That gives you a straightforward choice. Weekday lunchtime, roughly noon to two, is when it feels like a market: full of traders, City workers spilling out of the Lamb with pints, food counters running. Early Sunday morning is when it photographs best, because the avenues are empty and the low light comes straight down the length of the cross. Christmas, when the ironwork is hung with lights and greenery, is the other high point of the year.

Practical notes. Entry is free and there is no ticketing of any kind, despite what some tour operators imply. Step-free access is possible from Gracechurch Street, though the cobbles are rough throughout. If you are building a walking route, Lloyd's of London is immediately outside the eastern exit, the Roman amphitheatre remains under the Guildhall Art Gallery are ten minutes north-west, and the Monument to the Great Fire is ten minutes south-west. Photographers should bring something wide: the avenues are narrow and the best angle on the painted roof is from the crossing looking up and out towards the Gracechurch Street arch.