In this Dwarf cave you can hire dwarfs of different types. Each dwarf mines special crystals which can be sold in "Trade shop" and exchanged to real money. Each dwarf gives different quantity of crystals, and the more expensive he is, the more crystals he will get. You can hire any number of dwarf, they don't die, don't disappear and will be mining crystals constantly.
There are also extremely different types of dwrafs. Sleepy and Dopey. These dwarfs mine Payment Points instead of crystals. In order to collect mined PP come to the section "Storage".