This dungeon is located beneath Pollnivneach in the Kharidian Desert. You must wear a Masked Earmuffs or Slayer Helmet, as you need the protection of Earmuffs and Facemask (and possibly more) simultaneously. During the Smoking Kills quest you may only access the upper floor, but after the quest you can access the stairs.
The lower level has four sections behind barriers. To pass through the barriers you must defeat the respective slayer monster boss. You only have to defeat the boss once to gain access to the section. Kurask Overlord, Mightiest Turoth, Basilisk Boss and Monstrous Cave Crawler are the respective boss monsters. Each section contains portals which will transport you to the Rellekka Slayer Dungeon and the respective monster locations. These portals are one-way only.

Aberrant spectre (Level 96) Catolax Mighty Banshee (Level 90) Cave Crawler (Level 138) Kurask (Level 106) Turoth (Level 83-89) Basilisk (Level 61) Portal