I'm getting started with Web Map Service (WMS) integration.
https://www.ogc.org/standards/wms

The system seems extremely straightforward, but I can't find a single working example on the entire Internet of how to actually use one. My goal is to fetch terrain height and color maps at various levels of detail to feed into a streaming terrain system.

Does anyone here have experience with this type of technology? Can you jump-start my learning process here? Thanks in advance.

You are probably not going to find too many(if any) public examples of such an integration. However, its not that to difficult to get started. You can either roll your own WMS tile downloading service via libcurl or you can use an existing geospatial library such as GDAL to handle the WMS queries and tile download. GDAL does have API hooks to retrieve the raster data from such queries but it up to the application to interpret that data. Also keep in mind that most of the data is geo-referenced so should be easy to marry up the different raster data type providing you have a handle on working in those coordinate system( which probably will need conversion to your renderer coord sys.)

I figured it all out. Strange that this information is treated as if it is some secret no one wants to talk about.