Test your Parseltongue skills at the Reptile House of the London Zoo. In both the books and films, Harry first discovers his powers when he befriends a boa constrictor at the zoo nestled in Regent's Park, setting it loose on his cousin Dudley. The rest as they say is history.
7 Stoney Street
Start tapping bricks with your wand, or if desperation requires, your pink umbrella. Located in a shoot-off street from London's Borough Market, 7 Stoney Street served as one of two exterior locations for the Leaky Cauldron Pub.
Leadenhall Market may look ordinary, but that's only because you haven't Floo'd in. One of the oldest markets in London, Leadenhall first opened its doors in the 14th century. While it was historically famous for selling food stuffs, Leadenhall graduated to stranger merchandise when it became the double for Diagon Alley. It also served as a second filming location for the Leaky Cauldron.
King's Cross Station
Bonus: J.K. Rowling's parents met on a train from London, King's Cross to Scotland in 1945, so literally and figuratively, the magic began here!
St. Pancras International Station
Pop quiz: can you use Polyjuice Potion on a building? All signs point to yes, since The King's Cross you see in the films is actually the station's very own next-door neighbour, the St. Pancras International Station and Hotel. Scenic planners thought the architecture of St. Pancras better suited the aesthetic of the films. The filmed version of Harry's encounter with Dumbledore in Deathy Hallows is likely styled after the St. Pancras interior instead of King's Cross as well.
Exhibition Hall, Australia House
Australia House is the basis of the exterior for Gringotts Wizarding Bank in several Harry Potter films, and much of its interior is used for the bank as well. It's probably not worth the risk to break in and find out, just in case there are dragons and Goblin locks beneath its tame surface.
Canary Wharf/London Bridge/HMS Belfast
The skyline of Canary Wharf along with London sight-seeing staples, Tower Bridge and the HMS Belfast, make brief cameos in Harry Potter and the Deathly Hallows. Harry and Hagrid fly over head on motorbike, pursued by Voldemort and a gang of Death Eaters. Presumably these bright city lights were some of Hedwig's last sights. RIP.
Muggles aren't the only ones to locate vital government facilities around Whitehall. Here you'll find much of the exterior of the Ministry of Magic as seen on film in Harry Potter and the Order of the Phoenix and Harry Potter and the Deathly Hallows. Somewhere, just off the main road, is the stockroom where Harry, Ron, and Hermione stashed some knocked-out Ministry employees so they could snatch a Horcrux from Professor Umbridge.
If you've got the tiniest drop of magical blood in your veins, maybe you can confirm or deny the rumours that St. Mungo's Hospital for Magical Maladies is tucked into a side street in the Holborn area. The hospital never appears on film, but we know from the books that it's tucked away among red-bricked faced buildings. Could this facade around the corner from BuzzFeed UK be a Wizarding World front?
If you happen to find an abandoned Purge and Dowes, Ltd. department store but no hospital, then congratulations! You're at exactly the right spot, but condolences, as this means you can officially rule yourself a Muggle.
Claremont Square, Islington
You'll need to be a Secret Keeper to find this one, but you can still enjoy the atmosphere of Claremont Square, where the 12 Grimmauld Place exterior shots were filmed.
Vauxhall Bridge Road
If you fancy starting a journal where you can later store a part of your soul after committing heinous crimes, look no further than Tom Riddle's go-to shopping spot on Vauxhall Bridge Road.
Here's an origin story waiting to happen. Wool's Orphanage was home to a young Tom Riddle. While it can't be said for certain, rumour has it that before it burned down, the children's home could be found in the South Lambeth area.
Houses of Parliament
Westminster Underground Station
If you must travel like a Muggle, Arthur Weasley would recommend using Westminster Underground Station to reach the Ministry of Magic. To attend Harry's Underage Magic trial in Harry Potter and the Order of the Phoenix, Arthur and Harry play it safe using Muggle transport, and come to the universal conclusion that paper tickets are a pain.
Great Scotland Yard
Pick the most secluded phone booth around Great Scotland Yard and dial in to see if you might be sucked down into the Ministry of Magic, which is buried deep under the ground anyone in SW1 is standing on.
He's back! The film version of Harry Potter and the Half-Blood Prince opens in full swing, when Death Eaters destroy the modern footbridge in an act of terrorism on Muggles.
Piccadilly Circus/Tottenham Court Road/Shaftesbury Avenue
Hermione used to go to the theatre on Tottenham Court Road with her parents, and she whisks herself, Harry, and Ron to London's there on a quick escape early in the Deathly Hallows book. However, in the film, she takes them to nearby Shaftesbury Avenue instead. To muddle things further, the Shaftesbury-Avenue-in-lieu-of-Tottenham-Court-Road scene was in fact filmed on Piccadilly Circus. Bonus: Have a look in this area for Cafe Attack, where the trio holed up to hide in the film.
Gentlemen's Toilet, Horse Guard's Avenue
Hope you've perfected your Scourging Spell; you'll be needing it! After Voldemort's return, security measures increased and as opposed to apparating or Flooing to work, employees of the Ministry flushed themselves to work via the men's toilets near Horse Guard's Avenue.
For the keenest pilgrims: Plan a day trip to Watford for the Harry Potter Studios Tour. Everything that can't be found on location in London or elsewhere in the UK is tucked away at Warner Brother's extensive exhibit, and is just an Overground trip away.