Shau Kei Wan
Shau Kei Wan on the MTR Island Line is very much off the beaten track, but worth going out of your way for due to the Museum of Coastal Defence. Given the obscure name, you might not think you’ll be interested, but this is a gem of a museum and you’ll almost certainly enjoy yourself more than you expect. It also provides good views of the harbor it was built to protect.
One good way to make the most of a visit here is to arrive by tram - see the A Day Riding the Trams itinerary.