London: Imperial City

Welcome to London. From Heathrow, the Heathrow Express (15 min to Paddington) or the Piccadilly Line (1h, cheaper) take you to the center.

Your first walk is through Westminster: Big Ben, Westminster Abbey, Buckingham Palace and St. James's Park. If you arrive before 11 AM, you can see the Changing of the Guard (Mon, Wed, Fri and Sun).

Tip: Get an Oyster Card or use your contactless card; London transport is pricey but has a daily cap.

Magical day: Warner Bros. Studio Tour - The Making of Harry Potter. Booking required (sells out weeks in advance). The bus from Watford Junction takes 15 min.

You'll see the Great Hall, Diagon Alley, the Hogwarts Express and incredible models. Allow at least 4 hours. The shop is huge and dangerous for your wallet.

Tip: Arrive 20 min before your entry time; there are queues for the bus and to access the studios.

Last day. Notting Hill is London's most colorful neighborhood: pastel houses, Portobello Market (Saturdays are best) and independent bookshops.

Walk through Hyde Park to say goodbye to the city. If you have time, the London Eye offers 360-degree views of the whole city (30 min ride).

Tip: Portobello Market has the best prices at the far end, away from the Notting Hill Gate entrance; walk to the end.