A sinkhole is a natural phenomenon that occurs in certain types of land formations called karst. Karst is a landscape characterized by soluble rocks such as limestone, gypsum, or dolomite. These rocks contain sizeable underground cavities and channels formed by the dissolution of the rock over time due to the action of water. When the roof of one of these cavities collapses, it creates a sinkhole on the surface. Sinkholes can vary in size, from small depressions to massive craters that can destroy buildings and infrastructure.

Options 1, 2, and 3 (plain, desert, tundra) are not correct because sinkholes are not specific to these types of environments. Sinkholes can occur in various locations with karst topography, irrespective of the surrounding plain, desert, or tundra landscape.