Definitely by hunting.
Where should you hunt? In the area called Guzzlemaw Valley, here:
In this are, there some piles of bone which you can click, we call them "horns". 
When you click it, you have a 50% chance of getting an item called: Crude Horn of Bone 
or 50% chance of spawning a Guzzlemaw 
.
Your mission here is to gather as many Crude Horns of Bone as possible. At the same time will need an item called Mouthpiece for a Horn 
this one needs to be bought or collected near roshamuul boat (1 per day per character).
When you have both items, you should use on in the other and you will create the Crude Horn with Mouthpiece 
you should run to roshamuul wall and use that item there (it will crack the wall) :
For each item that you use in the wall, you will get 100 Inquisition Gold, which you can trade for a Cluster of Solace at the NPC Sandomo, near Roshamuul Boat.
Hi -> Book -> Trade -> n° of clusters
Also, each Frazzlemaw and each Silencer killed will grant you 1 Inquisition Gold each. If you happen to kill Sight of Surrender, then it will grant you 10 Inquisition Gold.
Source: https://www.tibiawiki.com.br/wiki/Roshamuul_(Lower_Roshamuul)_Quest#The_Walls_of_Roshamuul
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