Begun by William the Conqueror in 1068 on the site of the Roman fortress, Lincoln Castle is one of the best-preserved Norman castles in England. The complete circuit of walls — nearly half a kilometre — can be walked all the way around, with panoramic views into the city and out across the Wolds.
Inside the walls are several distinct buildings: the Lucy Tower (the older Norman keep, full of executed prisoners' graves), the Observatory Tower, the Victorian prison with its astonishing chapel of separate-cell pews, and a purpose-built underground vault holding one of four surviving original copies of the 1215 Magna Carta, alongside the slightly later Charter of the Forest. The combined exhibition on the two great charters is excellent. Single ticket covers walls, prison, and the Magna Carta vault.