Overall, I give this four stars.
The Mangrove Nature Reserve (officially called Hongshulin Reserve) connects many parks along the shore which forms a pretty large area. It is clean with many facilities such as toilets, restaurants and tuck shops scattered around and is pretty convenient.
Along the shore, there is a nice view of Hong Kong, which is just opposite of where you'll be standing.
I strongly recommend a bike ride. The price is reasonable and the bike lane is long and comfortable, with a nicely laid flat road which passes by the Universiade Sports Stadium and through many other parks. There is a soft breeze as you're by the sea so the temperature will not make a ride too difficult.
I would recommend a three-hour visit starting sometime around 3 or 4 to avoid the sun so cycling or hiking will be more comfortable.
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