Crystal Skull

While visiting a new world, the team discovers a huge pyramid, empty but for a central platform above a vast abyss, accessible by a single walkway. Upon the platform is a skull fashioned from pink crystal, that Daniel cannot resist looking into - at which point he disappears. Unable to locate Dr Jackson, SG-1 return to Earth hoping to find a way to retrieve their lost friend. The only clue appears to be a similar skull found on Earth by Dr Jackson's grandfather many years before...