The Tomb of Catherby

Opening the Tomb
To start the quest, head to Catherby and walk a little north until you see Asgarnia Smith. Talk to him to start.
 * Player: Hello there.
 * Asgarnia: This is amazing! Do you know what we have discovered!
 * Player: Wait, what?
 * Asgarnia: Fame! Fortune! Ten Museum Kudos! And... oh, sorry there.
 * Player: What did you discover?
 * Asgarnia: A tomb belonging to an ancient warrior!
 * Player: Is there any way I could help you?
 * Asgarnia: Actually, there is. But I don't think you're qualified.
 * Player: Hey! I actually worked with the Dig Site in Varrock.
 * Asgarnia: Hmm, that changes things.
 * Player: So, can I help?
 * Asgarnia: Yes. I need you to explore the catacombs beneath the mound here.

Open the trapdoor and climb down. Inside you see you are inside a thin tunnel. You must equip a Seer's headbands in order to proceed. At the end of the tunnel you find a small door which is jammed. If you have 67 Strength you may open it. After you open it, you find yourself in a large cavern.

Go around and turn on 5 switches which are found around the cavern. Once you have done this you do not require the headband anymore. Go the end of the cavern and attempt to open the large doors. You cannot, so Asgarnia will ask you to make an explosive potion, but it must be more powerful than the one from the Dig Site.

Making the Potion
Get out the tomb and go to Varrock. There, mine five lead. This requires 50 Mining and you must be wearing hard leather gloves. After this, go to Seers' Village and enter the Elemental Workshop. Head the second level and operate the machinery. This creates a primed lead bar. After this, use your hammer on it. It turns into primed lead dust. Add this to a vial of water to complete one part of the potion.

Now, you must get some chemicals. Head to the Poison Waste south of Isafdar and collect five Poisonous tars. After this, go to a churn and churn the tars and place it in a bucket. Finally, go to Keldagrim and ask Veldaban how the cannons work. He will tell you they require gunpowder. He will tell you to get him 28 coal and he will give you gunpowder.