The Mole, at the end of the Aramoana peninsula, is a 1-km-long (½-mi-long) breakwater protecting the entrance to Otago Harbour.
Dive Otago. A dozen or so small ships were sunk between 1920 and 1950 to protect the breakwater from the relentless Southern Ocean. You can check these ships out, and the tall kelp forest that protects them, with Dive Otago, which run trips when the weather allows. 2 Wharf St., Dunedin.