The Ceremony of the Dues
One of the more obscure but fun ceremonies, which has only been going on for the last 750 years, is the Ceremony of the Dues. The captain of every navy vessel entering the Pool of London takes a barrel of rum across to the man in charge of the Tower of London, all done with pomp and ceremony. Happens about once a year.
HMS Northumberland was accompanying the Zong, so the ceremony took place Staurday at 12 noon. Unfortunately I couldn't wait around to see it, so pictures of the preparation outside the Tower of London are all I have.