Borrevannet is a 4 km long, nutrient-rich lake near the fjord by Horten. It is bordered with cultivated fields and mixed woods, with spruce dominating in the north and tall, mature deciduous trees in the south. In the south end of the lake is Vassbånn, a marshy area with birch and willow scrub and reed beds, framed by dykes in order to keep the lake from flooding the surrounding farmland. In late spring and early summer, the earscape is dominated by several tens of male Thrush Nightinggale singing from the undergrowth. It is also one of the best general birding areas in SE Norway. The main entrance to the area is from the golf club parking, from where a path leads down to the tower hide.