To punish those who committed crimes against the Crown, they were sent to the Tower of London, a fortress and castle. High treason and piracy were among the very few convictions which could put a man in the Tower. Save onto the gallows or the block, there is generally no way out, once you are immured in this structure. There are already discussions underway to make it more 'financially self-sustaining', though this will not involve selling off the Crown Jewels. Certain Beefeaters, however, fear a change of diet.