Calcinator

The calcinator is a resource processor that creates resources from Sulphur.
The first step it to climb the ladder on the west side of the Calcinator, and deposit 20 Sulphur ore into the pile. You'll then need to add 10 Sulphur residue, and light the pile from the bottom with a Tinderbox. This will grant you 35 Firemaking xp.
The pile will burn for 15 minutes, and at the end of the process you'll be able to extract pure sulphur from the pile with level 40 xp.
Harvesting the Sulphur from the Calcinator yields 15 xp.
Careful not to stand too close to the fire, while its burning as it will damage the player saying you're too close to it.