This illustration is testing a methodology of creating a rich three dimensional model using extremely basic input, such as a basic hand-drawn map. A high quality version of the map used in this example is available at CaveAtlas.com:
Summary: The original graphic was georeferenced into a geographic information system. 83 depth values across the Peacock Springs State Park cave system were recorded and used to create a rough digital surface interpolation. The main cave passages were digitized into a polygon coverage. The spatially referenced graphic and the cave passages are projected together, using the interpolated surface as base heights.
Unfortunately, few cave ceiling heights are available in this map, so an artificial height of 5 feet is added evenly across the entire cave system to illustrate the 3D "cave" however it would be simple enough to add that information to create a more realistic depiction of tunnel size.