Maithon Dam is a large Damodar Valley Corporation reservoir on the Barakar River, about 50 km from Dhanbad. The draw is simple but real: open water, low hills, islands, and boating in a region better known for mines and power plants.
It works best as a half-day trip by car. The engineering is part of the interest, but most travellers come for the lake air and the wide view across the water.