A sinkhole is a dissolution feature caused by the chemical weathering of limestone.  As limestone bedrock is chemcially weathered, cavities form.  These cavities often collapse and result in sinkholes on the surface.  Sinkholes are denoted with close contours with inward facing hatchers on the contour lines.  In the center of the above topographical map is a large sinkhole.

Below one can see a three dimensional representation of the above sinkhole.

In the image below the aerial photograph over the sinkhole has been draped over a three dimensional surface.  The contour lines have then been drapped over the surface of the sinkhole to illuminate its shape.