Shing Mun Reservoir offers some nice hiking, with both relatively flat and steeper options. The one I’ve done a couple of times is very relaxed and easy 8km going around the reservoir. It starts from the Shing Mun reservoir mini bus stop going towards the Pineapple dam. There the route follows first Wilson Trail 7 until the northern end of the reservoir, from where I’ve taken the road on the other side back to the same bus stop. Half way back on the road, you can either continue on the road or take the Pineapple dam nature trail going on the shore of the reservoir.
One thing to note on this trail that especially towards the end there’s a lot of moneys which will steel everything they can – especially if it shiny. So hold on to your phones and hide the food!