Craftopia

Locate a dungeon portal on your island and enter inside.

The final room will contain one of three randomized bosses. You are looking for the Ancient Golem; and their difficulty is based on which island you entered the dungeon from. Doing this on the beginner island is preferable as the Ancient Golem won't deal as much damage and won't have as much health.

It's recommended to learn the combat dodge to quickly position behind pillars for protection against its lasers. It's also helpful when it begins to spin, as maneuvering the boss into the pillars will leave it stunned for a few moments, giving you ample time to melee it down.

From personal experience, using a copper bow with standard arrows was enough. Fire at the blue weak-spot and it should only take you a few shots before it dies. If you're attempting this on higher difficulty islands, you'll likely want to prepare a bit more with buff meals, better armor, and more powerful weapons.