What is the fastest way to cool hot soup?
Ice bath.

Put a bunch of ice in your sink or in a container large enough to place your soup pot in.  Add enough water to cover the ice.  If the soup pot is large or wide, you can speed up the cooling by periodically stirring it: this is particularly important for thicker soups or stews, where the middle section of a pot can stay warm for a long time.  Or, for maximum cooling, break up the soup into smaller -- preferably more shallow -- containers first and then place them in the ice bath (though this isn't generally necessary if you're using ice).

If you don't have that much ice, you can use a cold tap water bath to at least get it down to near room temperature before refrigerating.  But you will need to replace the water frequently for fast cooling.

(Unless you're breaking up the soup into smaller containers first, I would strongly recommend an ice bath over simply putting a large pot in the refrigerator.  It can take many hours for the contents of a large pot to cool completely in a refrigerator, which can be a food safety hazard.  If you do use the refrigerator alone, put into smaller containers and don't stack them to allow air circulation, and obviously don't place them next to highly perishable foods like raw meat, etc.)