Built from 1830 to 1831, this 12-sided stone prison is WA's oldest surviving building. It was the site of the colony's first hangings, and was later used for holding Aboriginal people before they were taken to Rottnest Island. On the hilltop outside is the Signal Station, where at 1pm daily a time ball and cannon blast were used to alert seamen to the correct time. The ceremony is re-enacted daily; book ahead if you want to fire the cannon.
To the Indigenous Noongar people, it's a sacred site because of the number of their people killed while incarcerated here. Freedom fighter Yagan was held here briefly in 1832. Beneath is an impressive 1837 Whalers' Tunnel carved through sandstone and used for accessing Bathers Beach, where whales were landed and processed.
