Big Ben & Houses of Parliament: The iconic clock tower on the Thames. Free to photograph from Westminster Bridge.
Tower of London: Home to the Crown Jewels. Book online to skip queues (£33 adults). Allow 3 hours.
Buckingham Palace: Watch the Changing of the Guard (free, 11am most days). State Rooms open in summer (£30).
Tower Bridge: Free to walk across; the Exhibition costs £11.40 with stunning glass-floor views.
The London Eye: 30-minute ride with panoramic views. Book online for £30+ and skip the queue.