West from Chalong, on the way to Radar hill, there's a huge construction site. Abandoned. What did they try to build here?

Sorry if I am asking about smth well-known, I'm a novice here

Just guessing:

its not an abandonded construktion site, but a former tin mine.

Up to the late last century there was tin mining in Phuket.

No, not a former tin mine. It's actually a new water reservoir that's being constructed (work has been ongoing for about the last 4 or 5 years). There is now a decent tarmac road that goes around the area (2 small sections of about 80 metres each yet to be completed). Once it's finished, the peripheral land will be highly desirable (and expensive) for sure, as good views out across Ao Chalong.

Thanks!