Ruins of Unte: How to wake up the Furnace Golem - Shadow of the Erdtree (DLC) - Elden Ring 

To get inside the Ruins of Unte you need to move the deactivated Furnace Golem. To do that, you need to activate it, aka wake him up. Then he will fight you. But by now, you know what to do!
All you need to do, really, is to throw a hefty fire pot inside is furnace basket above his head. You get a Hefty Furnace Pot by crafting it. You get the recipe called Greater Potentate's Cookbook [2] at the Run-Down Traveler’s Rest location beneath the bridge in Gravesite Plain.