The walls of The Tower are as much as fifteen feet thick.
The Imperial State Crown leaves the treasure house once per year, to be worn by the monarch at the state opening of the UK Parliament. For the rest of the year it is on display in the Tower treasure house for public viewing along with the other items in the Royal Jewels Collection.
George IV, wanting a new crown for his July 1821 coronation, could not afford the cost, so he contracted with the Crown Jewelers to rent the diamonds for his new crown, at a cost of 10% of the purchase price per year, or £6,525.
The Tower of London has been open to tourists for literally hundreds of years. Up to 46,000 people visit the Tower of London each week, or about 2.3 million per year.
The Tower's official title is "Her Majesty's Royal Palace and Fortress, The Tower of London."