Pancharevo lake is located about 15km south of Sofia on the way to Borovets resort in Rila mountain.
The lake is artificial and is 5km long. Many Sofians like to go there in the weekend and just walk around. The place is also good for different water sports like rowing and water skiing. Paddle boats can be hired. Around the lake you will also find cafes and restaurants.
If you want you can have a look at some of the pictures I have made there: