The Eastern State Penitentiary is a very popular former prison in Philadelphia known for its architecture and strict discipline. A very interesting audio guided tour leads you through the endless, naturally- lit passages of the prison explaining the history, design, cell types and a lot more. More information. 

Some photographs from my visit:

c (2 of 9)

d (1 of 3)

d (2 of 3)  c (7 of 9)

c (1 of 9)

d (3 of 3)  c (4 of 9)

c (5 of 9)

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