Ruins

The Visitors have left not much else but bizarre structures behind. The ruins are mainly composed of thick walls of blue-gray stone. They are also the only source of Embers, Objects of Power, and metals. Only items with extreme longevity have endured the test of time since the fall of their civilization, everything else is long decomposed. Historians and adventurers classify them according to their shape and structure: Ruins not belonging to either of those categories also exist, but aren't very notable or well preserved.
 * Anchorpost: an intricately decorated obelisk with a circular platform surrounding it. They are rare, only five are known, and four intact. Their tendency to pull in Outsiders makes them the sole active Visitor structure;
 * Auditorium: a large, circular hall with a depression in the middle with shattered glass panes;
 * Cathedral: tall building with long-gone windows, thin columns supporting the arched ceiling;
 * Canal: open-topped and fully closed tunnels, currently used as water reservoirs.

The Library of Truth
A place which only exists in legend so far, the Library of Truth is said to be a completely pristine Auditorium that holds all the knowledge in the universe. However, no knowledge may leave the building, and those who claim to have been there also claim to have had their memories erased.