Begin in the Square Mile. Here, the Romans built a wall. The Victorians built palaces of industry. The glass-and-steel towers of the 21st century now lean over narrow, cobbled lanes named "Pudding Lane" (where the Great Fire started) or "Bread Street." You can touch a stone from 100 AD and, thirty feet later, step into a Michelin-starred restaurant that used to be a warehouse for tobacco.
You cannot write about London without addressing the weather, but not as a complaint. The weather is the stage manager. The light in London is unique: soft, grey, pearlescent. It makes the red telephone boxes scream with colour. It turns the rain on a window into cinema.
There is a moment, usually just as the Tube train rattles above ground between stations, when London reveals itself. You see the jagged silhouette: the Gherkin next to a medieval church spire, the Shard piercing low clouds like a shard of glass, and the London Eye turning its slow, mechanical blink over the grey silk of the Thames.