Heritage Open Day: Free museum entry from 6th-15th September! Come down from 6th-15th September to explore the history of Horsepower at Hampshire's only museum of Cavalry. Our usual fee for entry is being waved for the duration of the Heritage Open Days celebrations. From 6th-15th September all visitors will be allowed into the museum free of charge. Come down from 6th-15th September to explore the over 300 years of Horsepower history at Hampshire's only museum of Cavalry.