There is spring fed lake in Bitsa Park.
Most of the locals do not know about the lake and spend time at Bitsa river.
You also won't see it on the map:
The lake is deep and water is always cold in the summer:
And never freezes in the winter (UPD: it is a lie - it freezes in winter) :
Swimming there is like a swimming in the mountain river.
It recharges you every time.