Dark Gateway

Description
The Dark Gateway is the location from which the creatures of the Underworld will emerge, to enter in the service of the Underlord who has claimed the Dark Gateway as their own. Remember, though, that each Dark Portal will only be able to summon a certain amount of minions, before you must seek out more in order to grow your Infernal Army.

Also, never forget that there are other ways to call dark beings to your service...