Dark Prince's Realm

The final domain in the Realm of Chaos belongs to Slaanesh, the decadent Dark Prince of Chaos. Slaanesh's realm is the smallest corner of the infernal regions, for he is the youngest of the Chaos Gods, and as yet his power is much overshadowed by his brothers. 1a

Places of Note

 * Causeway of Secrets
 * Grove of the Dark Maiden
 * Marcher Fortress
 * Palace of Slaanesh -- Slaanesh's seat of power
 * Six Circles of Seduction
 * Slaanesh Marches
 * Vale of Creatures
 * Vermillion Caverns

Source
Warhammer Armies: Daemons of Chaos (8th Edition) -- pg. 12