London is one of my favorite cities on the planet - in fact, if it was easy to get a UK Visa, I'd probably be living there. My friends wanted to know what my perfect 24 hours in London would be, so based on my vast experience in the city between studying abroad there for a semester and trying to visit at least once a year, this is what I came up with of some ideas of things to do!
While the London Eye is a can't-miss for most, it is quite pricey, and lines can be long during peak travel times. Instead, a recommend booking a visit to the Sky Garden, which is absolutely free and gives amazing panoramic views of the Tower of London, Tower Bridge, The Gherkin, The Shard and more. Alternatively, for those willing to spend a bit more money, The Shard is quite an amazing view if the weather is good. For the more adventurous types, you can also climb the outside of the dome of the O2 Arena at Up at the O2 for quite a unique city view (think like the Sydney Harbour Bridge climb).
There are many great places to do afternoon tea in London from Harrod's to Kensington Palace, but my favorite has to be Sketch. You will definitely need a reservation, and it isn't cheap, but there is nothing quite like taking tea in such a pink, artsy room as the Gallery. Also, their bathroom is made of space pods. 'Nuff said. Sketch is located in the Oxford Street and Regent Street area, a prominent place to shop in London, so after you eat you can head over to Selfridge's, Topshop, and more to feed your shopping addiction. My favorite street to shop on in that area is Carnaby Street, which has an awesome wacky shoe store called Irregular Choice. Also, it's a short walk to Piccadilly Circus, home of West End theatre productions such as Les Misérables and loads more.
Museum Speed Round! Seeing all the museums in London would take months and months, trust me, so if you only had a day, I'd pick one at most. The Tate Modern is one of my favorite museums in town for its modern art collection and amazing rooftops views. For a bit more history, one could spend hours at The British Museum. The V&A Museum is another favorite of mine - I once saw a special David Bowie exhibit there! Other museums include the Science Museum, Natural History Museum, National Gallery, London Transport Museum (and visit Covent Garden while you're there), and Imperial War Museum. Always check for special exhibits that may be in town too, like this one I saw of Yayoi Kusama's Mirror Rooms at the Victoria Miro.
Another option for the day could be immersing yourself in the world of Harry Potter. The Warner Bros. Studio Tour London is a train ride outside of the city and requires advanced booking, but is a must-do for any major fan. I recommend giving yourself AT LEAST 4 hours to explore the studios, where you'll see everything from the Great Hall of Hogwarts to the Potions Classroom and an animatronic Hagrid head. Oh, and don't forget to drink some butterbeer while you're at it! For those who want to spend time exploring the Harry Potter sights in London proper, there are many walking tours that will help you with that, like Tour for Muggles. Platform 9 3/4 is easy and free to visit if you happen to be passing by King's Cross Station, perhaps on your way the The British Museum nearby.
Obviously, I've only covered a fraction of what there is to do in London. There are markets galore, amazing dining, historical sites, Buckingham Palace, etc. You could do something wacky like Secret Cinema or spend the day simply walking through Hyde Park. I could probably write an entire book on all the possibilities of things there are to see, but I hope this guide has been somewhat helpful in recommending to you, dear Reader, what you should do in this wonderful city. Anything I missed that you want to recommend to others? Just mention it in the comments below!