OGC WMS Demo and Reference Server
Please check the OGC Schools repository on GitHub for an introduction to this server: https://github.com/7o9/ogc_school/blob/master/implementations/metaspatial.rst
There are two map image references below. The left (or upper) version of the map is a static image. The right (or lower) image has been rendered dynamically when this page was first requested. If you can see both images then the server is up and running. If the right (or lower) image is missing then the server is down for maintenance.
OGC Reference and Demo Server: Dynamic Image
Both images have been rendered using the WMS GetMap call: