Coldbath Fields Prison
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Coldbath Fields Prison, also formerly known as the Middlesex House of Correction and Clerkenwell Gaol and informally known as the Steel, was a prison in the Mount Pleasant area of Clerkenwell, London. Founded in the reign of James I (1603–1625) it was completely rebuilt in 1794 and extended in 1850. It housed prisoners on short sentences of up to two years. Blocks emerged to segregate felons, misdemeanants and vagrants. (Wikipedia)
 
Birds eye view of en:Coldbath Fields Prison in The criminal prisons of London, and scenes of prison life (1864) by en:Henry Mayhew (d. 1887) & John Binny. The main felons block is on the left, the vagrants block was the "half cartwheel" bottom left, the misdemeanants block centre right.

Clerkenwell 101
40 Coldbath Fields Prison at Mount Pleasant, was the very first prison to introduce the treadmill, back in the 1830s. Prisoners were allowed five minutes off for every 10 minutes on, over an eight hour shift. This is the equivalent of climbing 8,000 feet. It’s like climbing Snowdon twice a day but with a less interesting view. It took a few years for the authorities to actually use the treadmill to power the prison itself. Before that, the prisoners were doing it for the sheer fun.