Barrows is a Minigame accessible via Minigame Teleport. It's really easy to kill all the brothers, So I'd recommend this guide for level 100+ (I'm level 138). On 10/3/2015 they raised the rate of getting a barrows item.
What is barrows?
A Minigame in which you kill 6 Barrows Brothers, Including
Guthan The Infested (Use Protect from Melee)
Karil The Tainted (Use Protect from Ranged)
Torag The Corrupted (Use protect from Melee)
Ahrim the Blighted (User Protect from Magic)
Verac the Defiled (Use Protect From Melee)
Dharok the Wretched (Use Protect from Melee)
For my Inventory I choose to have Super Att/str/def and lots of Super Restore Potions (to bump up prayer, and therefore not having to bank as often) And a SHOVEL. Bring a shovel.
I do the minigame in the following order, and I recommend you do the same. (On top of each brother's cavern you need to dig to go into the cavern, then you open the coffin)
Guthan, Karil, Torag, Ahrim, Verac, and Dharok last because he is ALWAYS the boss.
3) The Boss.
Dharok is always the boss, therefore that's why I kill in the order that I do.
Once you have killed all except Dharoks, When you click on his Coffin, it will ask you if you want to go the the Treasure Room, Press Yes, and Dharok will spawn. After you kill him, click on his Coffin, and select Yes again, which brings you to the treasure room.
4) The Loot.
Once you've followed steps 1-3, it will bring you to the treasure room. Open the chest, and see what you get!