A Lost Demention
Requirements:
78,179 gp

To start this quest you will need to find "a helmet of blue gold." This is a rune full helm and is found at the Varrok armour store. Trade Horvik to buy it. (It costs 78,165 gp, and currently buying it from Horvik is the only way to obtain it.)

After you have bought it you will need to talk to Simon. He is in Varrok just below the staff shop. Once you talk to him you will be teleported to a lost dimension.

Upon entering this lost dimension the riddle will pop up.

After this head north and then west into the market square and trade Larry. You will need to buy an onion, a tomato, and a knife. Then use the knife on the tomato and it will chop it up and put it in a bowl. You then need to use the onion on the tomato. You will end up with a bowl of "onion & tomato."

Once you have done this head east, then a little north and then west into the circle of buildings. You will see a witch named Aggie. Talk to her with you "onion & tomato" in your inventory.

Congratulations! Quest Complete!

Here's your reward!