After making your way up the Heights of Loneliness and learning Mason's story, you reach Zere Rocks.
This place is a perfect replica of Zere. It's as if someone used a copy machine--a Xerox machine, perhaps?--to create Zere Rocks. There isn't much to do here. Just go into the northeast house and read the books on the bookshelf to learn some new recipes. Then talk to the slime. Then go outside to start a boss battle.
Garth likes to cast Kabuff and Magic Barrier, which will make it take longer to defeat him. Otherwise, just attack until it dies. It drops a Terrible Tattoo after the battle, but don't equip it. It's cursed, which means that you won't be able to unequip it unless a priest performs Benediction on you. You can either pay money at a church to get a Benediction, or you can teach your Priest the Benediction skill by spending 28 points on the Faith skill tree.
You are better off saving the Terrible Tattoo to use it as an alchemy ingredient.
Afterward, go downstairs and talk to the ghost to receive a Fygg. Your next destination is Bloomingdale, which you can reach if you go south, then across the bridge, then west.