To get to Ghat by boat from Ankh-Morpork you must go via Cape Terror. Sir Samuel Vimes sent the Assassin the Hon Eustace Bassingly-Gore that way in chains. The terror is inspired by the fact that this is the closest point on the main continent to the rim, but unfortunately, all sea traffic between the whole Circle Sea area (including Ankh-Morpork) and Brindisi, Genua , and points Widdershins, must pass by it.
Also a reference to the Cape of Good Hope, so named because of the great optimism engendered by the opening of a sea route to India and the East - and the fact that you had to hope you survived going round it as the weather was and is so treacherous. The first European to reach the cape was the Portuguese explorer Bartolomeu Dias in 1488, who named it the "Cape of Storms" (Cabo das Tormentas). It was later renamed by John II of Portugal as "Cape of Good Hope" (Cabo da Boa Esperança).