There are some sinkholes visible at the so-called upper 'Eselsberg', located near the University of Ulm, Baden-Württemberg, Germany.
Dolines are sinkholes with shaft, funnel, or bowl shapes that commonly occur in karst landscapes. While larger sinkholes, e.g. in South America, can reach a diameter of 200m and a depth of 400m, the dolines you will see are of more moderate size.
Dolines form when rain water rich with carbonic acid seeps through cracks and fissures of limestone. The rain water initiates dissolution of the carbonic rock (corrosion), karst shafts form in the rock. Lime and looser materials are washed out with the rain water. This can lead to the formation of caves and cavities. If the ceilings of such cavities give way, material in the karst shafts slides down, resulting in the formation of a doline (sink) on the surface.