Boss Timers can be found here.
Black Desert Online World Boss Garmoth is located directly North of Duvencrune in Drieghan. Garmoth spawns every Sunday, Tuesday, and Thursday. Boss timers can be found by clicking on the world boss image above.
Garmoth raid begins with Garmoth spawning in the center of Garmoths Den. For the first thirty seconds Garmoth stand still and you will be able to attack. After this first sequence Garmoth will go up into the air. Next Garmoth will land and do two aoe's. Make sure you steer clear of the aoe's as they hit hard. Once this is done Garmoth will spawn katagums which you will have to defeat. Lastly Garmoth will go back to his original ground position where you can damage him. After this the cycle will repeat until Garmoth is defeated.
If you dont have the gear to fight Garmoth and you are scared of fighting you can always just get a hit on him and then stand far back so you cant get hit. By doing this you stay at a safe distance where you wont have a chance of dying.
Killing Garmoth gives you a chance of obtaining a Garmoths heart. These hearts are super rare and valuable going for 8bil, and greatly increasing your stats. The other possible loot is something called a belongings of an adventurer. These are also super rare and have a chance of dropping any accessory from the base version to tet!