If you grew up on the Harry Potter books (or even just read them to someone who did), the name Diagon Alley will no doubt ring a few bells. The fictional street is where Harry Potter and his friends go to buy their school supplies in the first book and it's a regular feature in all seven of the Harry Potter books.
Warner Bros. did an excellent job bringing our favourite Harry Potter locations to life, but you don't really get to see all the work the studio put in while watching the movies. The cameras move too fast to take in all of the detail and there are other things to pay attention to. Still, if you'd like a closer look at Diagon Alley, you can now explore it on your own time thanks to Google. The search giant has added the Warner Bros. set to Google Street View.
The official address for is "Warner Bros. Studio Tour London, Studio Tour Drive, Leavesden, Hertfordshire WD25 7LS," but you can find Diagon Alley through this direct link. Watch out for the scary figure in the shadows!
They're wizards, and as such there's no headaches involved in building shops in whatever whimsical shape they want. Not "physically possible"? magic. Not enough space? magic. Too hard to build odd shapes? magic. Basically their architects don't have engineers telling them what is or isn't possible/practical, because it's not an issue.
http://map.soso.com/#pano=10051550121021130922840&heading=354&pitch=-3&zoom=1 (Potala Palace, Tibet)