So, I tried to use a map with an Enum object (which I am told I can use as a datatype in the documentation), but it does not work.

Declaration in the class definition:

public enum Season {WINTER, SPRING}

Definition of Map in the constructor:

Map<Season,String> heatMap = new Map<Season,String> ();

Error: Compile Error: Map by CustomCon.Season not allowed at line 27 column 37