Biržai Regional Park

The region around Biržai is famous for its karst sinkholes, formed when underground water sources wash away the gypsum supporting the soil. More than 9000 of these holes, including the 12.6m-deep Cow's Cave (so-called because an unhappy bovine was swallowed up when it opened, 200 years ago) can be found in the area, many within the 146-sq-km regional park. The park office sells entry tickets and has more information on the topography, plus walks, tours and other activities.