Argentium, also known as Wheel World due to its shape, is the home planet of the Bem species. It is in the shape of an enormous wheel.
Sonic the Hedgehog visited Argentium while he was traveling through space, hoping to find a way to return to Mobius. However, when he arrived he was surprised to learn that he wasn't the only Mobian there: Tails' parents Amadeus and Rosemary Prower were also guests of the Bem, having been brought to Argentium by the Bem scientist Ceneca 9009. Because Ceneca 9009 had De-Roboticized Amadeus with her outlawed Robotizer machine, she was sentenced to life in prison. Sonic agreed to help her and the Prowers, but the only ship they were able to obtain could only take one of them back to Mobius. Despite his wish that one of the Prowers go, Sonic was the one, and he traveled through the artificial wormhole adjacent to Argentium.
Merlin Prower later came to Argentium with Sonic, Tails, and Knuckles the Echidna in tow to rescue Amadeus and Rosemary, only to find the planet torn by war between the Xorda and the Black Arms. Fortunately, neither of Tails' parents were harmed, and they all returned to Mobius safely carrying news of the war. Later, A.D.A.M.'s gathering of the Chaos Emeralds revealed that Argentium was the home of the Grey Emeralds, which were later fused together by Feist into a single gemstone.
- Argentium may have been inspired by Larry Nevin's novel Ringworld (which also inspired the Halo franchise).