The Crystal Golem is found in the Crystal Quarry Biome.
It is extremely dangerous, since it comes in large groups. But considering you have good equipment, it shouldn't be as much of a problem.
Ranged attacks are recommended, but if you play melee, hit with the sword, back up (and recommendably into a base), wait for distraction, swing, and repeat.
|Crystal Quarry Monsters|
|Crystal Slug - Crystal Bat - Crystal Golem - Crystallized Hero|