Hong Kong is a place you need to walk around. Even with its excellent transportation system, you need to put a lot into your legs. The city's structure is anything but flat, the paths guide you under and over the street level, intersecting shopping malls, going to another malls, creating parallel, somehow even more human space in contrast to the heavy car traffic on the ground, especially when used as a personal leisure place on the weekends.
The footbridges, walkways, tunnels, escalators, staircases, are a concrete and glass maze that is a pleasure to explore. You need to invest a quite amount of energy to move around and against the ongoing smog, but the city's energy will more than compensate your efforts, giving you places, people and food to discover and photogenic scenes every corner you go.