Mentioned by London City Calling
50 free things to do in London
"While visiting the historically important Tower of London does require a paid entrance ticket, the daily Ceremony of the Keys – the traditional ‘locking up’ of the Tower – is completely free to watch. At exactly 21:53 each evening, the Chief Yeoman Warder (or ‘Beefeater’) marches through the Tower carrying the Queen’s Keys. Escorted by four armed guards, he performs a series of specific rituals as he locks the gates to the Tower for the night before returning the keys to the Queen’s House at 10pm."