Causeway Bay Breakwater (1st generation) [1884-????]
I guessed this was a 20th Century construction, built after the 1906 typhoon. But it's much older. It's completion is noted in the Legislative Council meeting held on 28th Feb, 1884:
15. Adverting to other important public undertakings, which have received legislative sanction, I am glad to inform you that the Break-water at Causeway Bay, intended to form a harbour of refuge for the boat population during typhoons, has been satisfatorily completed within the amount originally estimated;
A map from 1889 (UK Nat. Archive ref: 1889 CO 700-HONG KONG AND CHINA7) shows the breakwater the same size & shape as in maps from the 1930s (eg Plate 3-5a, Mapping Hong Kong).