Eastern State Penitentiary was once the most famous and expensive prison in the world, but stands today in ruin, a haunting world of crumbling cellblocks and empty guard towers. Known for its grand architecture and strict discipline, this was the world's first true penitentiary: a prison designed to inspire penitence, or true regret, in the hearts of convicts. Its vaulted, sky-lit cells once held many of America's most notorious criminals, including bank robber ''Slick Willie'' Sutton and Al Capone. Tours today include the cellblocks, solitary punishment cells, Al Capone's Cell, and Death Row. A critically-acclaimed series of artists' installations is free with admission. Just five blocks from the Philadelphia Museum of Art.