The home of Mount Doom, where the ring of power was forged. A place where happiness has never visited nor tried to. The smells of reeking decay that swirls through the lands.
It all settles on the mind and translates into a forceful desire for Frodo to succeed. Mordor certainly helps in the reader wanting, no, needing the protagonist to accomplish his goal.
What fictitious world has hit you hard in the guts?