The Blue Lake is a karst lake that lies on the edge of town. A fascinating natural phenomenon, the lake has a depth of up to 147m (in 1914) which completely disappears in the summer, leaving a dry base that even holds football matches. The Blue Lake is guarded by a large crater which is up to 800 metres long and 500m2 wide. It is the natural swimming destination for the local people, a place to enjoy and respect nature.