This map is focused around a quick 4 player FFA. The only way to upgrade your creatures will be to reach the middle of the overworld and find a hillfort. The underground is somewhat plain and used only for finding extra resources and artifacts. Venturing down there with a low level hero with few creatures is a bad idea! Play PVP or against the AI. To win you need to defeat all the enemies.
In this map you won't be able to upgrade any creatures in your town but instead have to do it in the middle of the map at the hill forts. The underground passage will unlock some extra treasures and such. Advanced resources in middle.