It was a highly walled fortress, built atop a half-mile high mountain using extensive slave labor (for over a thousand years) and was home to Ctuchik, a Disciple of Torak. Rak Cthol was the spiritual headquarters of the Grolim priesthood. Rak Cthol's walls were described as being ten times to fifty times high than the walls of Vo Mimbre, and that people could see ten leagues in any direction from the walls.
As the chill breeze blew off the last of the haze, the shape of the city perched atop the crag began to emerge. The walls were as black as the sides of the pinnacle, and black turrets jutted out from them, seemingly at random. Dark spires rose within the walls, stabbing up into the evening sky like spears. There was a foreboding, evil air about the black city of the Grolims. It perched, brooding, atop its peak, looking out over the savage wasteland of sand, rock, and sulfur-reeking bogs that encircled it. The sun, sinking into the banks of cloud and ash along the jagged western rim of the wasteland, bathed the grim fortress above them in a sooty crimson glow. The walls of Rak Cthol seemed to bleed. It was as if all the blood that had been spilled on all the altars of Torak since the world began had been gathered together to stain the dread city above them and that all the oceans of the world would not be enough to wash it clean again. - Magician's Gambit