Everything tagged: trench

I attempt section 4 of the MacLehose Trail on the hottest Sunday of the year earlier.  I actually didn't make it but that's another story.  Before I quit and while I was on the way, I noticed in some places around Wong Chuk Yeung and beyond, there seemed to be trenches right next to the path.  I took this photo at around 22.406128, 114.262329:

There's a small building, several concrete structures, and many trenches. Does anyone know who built them, and what for?

Phil started off the investigation with this message: