One of a Kind

Needs Royal Court. "Mythological rarity" means the unique/historical artifacts - relics, famous gems, the crowns and weapons of dead kings - not the ordinary commission tiers. Start as an emperor for the best flow of inspired guests and the gold to indulge them, then sponsor characters with the Adventurer inspiration, favouring high-skill adventurers (skill drives both quality and the option to hunt something unique). It's RNG on what they bring home, so expect a few sponsorships before the special one lands. The same adventurer sets up They Belong in a Museum, and it all counts towards Inspirational.