Queen's 90th: What's happening and when?
21 April - The Queen will unveil a plaque on Windsor's Queen's Walkway, before lighting the first of a chain of beacons. Gun salutes will also be held across the UK
12-15 May - Celebrations featuring hundreds of horses and performers in the grounds of Windsor Castle
10 June - A national service of thanksgiving at St Paul's Cathedral
11 June - The annual Trooping the Colour at Horse Guards Parade
12 June - The Queen will host a street party for 10,000 people in the Mall
Posting this info I found on the BBC website. Nobody does pomp and circumstance better than the British so if in London or at Windsor during any of these ceremonies be prepared for large, respectful and exuberant crowds. God Save The Queen!