Sundovik is a right tributary of the Volga, 97 km long, in Bolshemurashkinsky and Lyskovsky District districts.
The workers’ settlement of Bolshoye Murashkino and the town of Lyskovo stand on the Sundovik.
The source lies east of the village of Kartamzovo, the mouth below Lyskovo.
There is little forest along the banks; the valley is up to 650 m wide, the slopes up to 30 m and gentle. The river is 15 - 35 m wide and up to 3 m deep, the banks steep, at places sheer.