Mother Shipton's Cave
Tucked away in beautiful woodland across the river from the center of town is the birthplace (according to local lore) of the titular 16th-century prophetess who supposedly foretold events such as the defeat of the Spanish Armada and the Great Fire of 1666. Next to the cave is the mineral-rich Petrifying Well, England's oldest entrance-charging tourist attraction (it's been selling tickets since 1630), famously able to petrify soft objects in three to five months.
