Learning about the Haunted Mine
Start the quest by speaking to The Zealot, whom is located just north of the mine. The Zealot will ask you to state your allegiance. Tell him you follow the path of Saradomin, then that you come seeking challenges and quests.
After The Zealot goes on about the haunted mine, ask if there is another entrance. He has come across a key. Ask him for the key and he will not budge on giving it to you. Your only chances of completing this quest is to pickpocket The Zealot. You will retrieve The Zealot's key.
Ladder after ladder
Head southwest of The Zealot and walk past many mine carts. Climb over the one which blocks your way. You now find yourself at the second entrance of the mine. "Crawl-down" the Cart Tunnel.
Once inside, follow the tracks west and continue past the ladder. "Crawl-through" the Cart tunnel at the end of the tracks. Now head south to the next tunnel and "Crawl-down". You are once again be inside the mine. Head northeast until you reach a ladder and climb down. Head east and climb down the first ladder you would pass.
After you climb down, you need to head northwest to the track with the moving cart on it. Now head south to the next ladder, but be careful not to get caught by the cart. Hide in the crevasses that are in the wall as the cart comes your direction. Climb down the ladder once you reach it.
Head west and pick some Glowing fungus from the water. There is a chance to fail later on in the quest, so pick more than one to be safe.
Next, walk north then west of the ladder, along the mine tracks and to a mine cart. Use the glowing fungus on the cart.
Adjusting the track
Head north from the Glowing fungus and find the Point Settings board. Compare the track junctions to the solution and then pull the appropriate levers to switch the junctions. You'll find levers A-E east of the board and levers F-K north. Afterward, put the minecart in motion by pushing the Start button on the Point Settings board. If done correctly, the cart will move toward the ladder. If not, the cart will go into the water and you'll have to restart. This means replacing the Glowing fungus in the cart too.
Now retrace your steps back to the first floor.
Climb down the ladder you originally passed. Head northeast and climb down the ladder. You now need to head northwest to yet again another ladder. Climb down, and walk to a mine cart. Search the cart and take the glowing fungus. Climb back up the ladder.
Head all the way east to another ladder and beware of the moving cart. Climb down the ladder. Head south through the wide tunnel until you come to some bronze piping, a lift, and a water valve. Try to turn the valve and find it's locked. This is where The Zealot's key comes in. Use it on the water valve and water will begin to flow.
Run to the lift on the other side of the water valve quickly. If you don't, a ghost will close the valve before you reach the lift. You will plunge down into a flooded chamber and swim over to safety.
Head south down the path until you reach a 2-way fork. Take the eastern path, head down the stairs, and prepare to fight! Head west through a door until you reach an Innocent-looking key. Attempt to take it and the Treus Dayth will appear. Treus Dayth is a special ghost whom can control his surroundings. He will not fight you; instead, he uses the objects inside his lair.
It is recommended that if you are a lower level player that you bring excess food, your best armour, and a strong weapon. Magic and range are not recommended to be used, but it is possible to kill him if you have a high enough level. Note: Protect from Range does not help.
Once you defeat him take the innocent-looking key and head back upstairs. You now need to head west to another set of stairs and head down them. Open the "Large Door" and head southeast. You reach a crystal outcrop. Use your chisel on it to receive a salve shard in your inventory. If you do not have a chisel, you can find one on the crates upstairs by the lift.