In this guide we will be making money of Big Bones from Hill Giants and from looting the Brass Key in the same area. First you will need to get one Brass Key from the Grand Exchange in order to enter the place we are going to.
Then you are going to make your way to a little house just to the West of the Cook’s Guild, slightly to the southwest of the Grand Exchange. Down here there are two good ways of making gold. The first is to kill the giants and loot the bones, the big bones are worth about 400gp each. The other way is to go straight from where you enter and into the first room to your right. There are a bunch of zombies here but just ignore them and loot the Brass Key on the ground there. It respawns quickly so just pick it up until your inventory is full. The Brass key is worth about 850 gold each. Doing this you can make up to 500k gold an hour.