Baldur's Gate 3

Tied to defeating the Adamantine Golem, you will find the forge in the Underdark; specifically, the Grymforge map, where the Duergar can be found. To get here, in the Underdark there is a weathered fishing village that is occupied by the Duergar that have been slaying Sovereign Spaw's colonists. Near the water's edge is a boat that you can actually commandeer to lead you back to where they came from, but not without a few interactions with another Duergar boat.

Once you've made it through the rough and scuff of the Grymforge, ascend to the upper walkways of the map, avoiding the traps and utilizing the levers, to go over their heads and make it to the far end of the walkway where it will eventually bend towards the forge. Along the way, you might find a few item moulds to fill in at the forge; grab whichever you want to eventually make, as well as once you've unlocked the Forge waypoint, you might be able to see a few huge deposits of Mithral.

At the forge, you need the following:
A weapon/armor mould to insert in the mould receptacle.
A chunk of Mithral, which the game provides two along the way, to be placed under the Forge Hammer

Pull the lever to the side to have the hammer strike the metal and lower the platform. Now, you'll need to heat the metal up, so open the lava vents and deal with the golem. After that, pull the hammer lever once more to obtain your item and this trophy.