Citadel of Silver Light

The Citadel of Silver Light was by Zola: "'Ooooh. And that's why no one's been able to find the Citadel of Silver Light. Amazing! it explains so much!'"

Possibly Relevant Outside Information
The Professors are reported to have given a travel information for Agatha: Paris, England, Africa, Skiffander(sic), and The Crystal Tower of Light(sic), in that order.