Stagg Mansion was the lavish, palatial estate of billionaire inventor Simon Stagg. Stagg lived at the manor along with his late wife Maya, his daughter Sapphire and his Neanderthal servant Java. Although the bulk of Stagg's scientific interests were conducted at Stagg Enterprises, he maintained his own private laboratory in the sub-levels of his mansion.
In this laboratory, Simon Stagg developed machines aimed at transforming Metamorpho - the Element Man back into his human form of Rex Mason. Stagg never truly wanted to help Mason though, and he only continued working on these projects out of love for his daughter, Sapphire. Stagg wanted Mason to remain in his elemental state, and to ensure his loyalty, he was able to control him through the Orb of Ra, which he kept closely guarded inside the mansion.
One of Stagg's former assistants, Kurt Vornak, once broke into the mansion and sabotaged Stagg's laboratory. The incident prompted a chemical explosion which transformed Vornak into a disembodied atomic energy man. 
When Metamorpho and Sapphire Stagg Mason gave birth to their metahuman son Joey, Simon created a technology advanced nursery so that he could monitor Joey's powers. Although Joey's powers were similar to his fathers, he had the added benefit of being able to alter the chemical structure of other objects, literally turning lead into gold. When Metamorpho learned that Simon was keeping Joey for his own egocentric purposes, he broke into the mansion, tore apart the laboratory and rescued him.