The land walls of Acre were strengthened by Ahmad Pasha al-Jazzar in the 1790s, with the help of a French engineer and, crucially, British naval support. They proved their worth in 1799 when Napoleon's army besieged the city for 61 days before retreating to Egypt — one of the few setbacks of the Napoleonic Wars in the East.
You can walk much of the wall perimeter for free. The seawall is particularly rewarding at sunset: the old fishing harbour lies below, with the open Mediterranean to the west. The Tower of Flies sits on a breakwater just offshore — a medieval Crusader tower that once controlled the harbour entrance with chains stretched across the water to prevent enemy ships from entering.