The First Weird Thing: A Plot Where the Party Discovers Earth

 I finally figured it out! My 12 Weird things will focus on 12 weird plots that can be used in the RPG of your choice. This first one is suitable for scifi in your prefered flavor and system:

Weird Plot One: The Party of Galactic Explorers Land on a Strange World - But it's Really Earth

So here's the premise, ripped straight from Planet of the Apes: the party belongs to an expedition which is surveying new star systems and looking for habitable worlds. They are part of an alliance of star systems united under a common galactic rulership, the Orion Consortium, so named for its center of power in the Orion Star Cluster. Their starship is a competent vessel with the resources (shuttles) to land on suitable planets. They have just discovered an inhabitable world with ideal gravity for Orions to dwell on.

Investigating the planet they discover that the world has traces of ancient, vast ruins that appear to have been abandoned tens of thousands of years ago. The curious thing is that no direct evidence can be found as to what catastrophe led to the sudden abandonment of this ancient civilization. Even more impressive, the planet's current sentient civilization has risen from the ashes of what came so long ago, and the strange aliens, a species which is (1D6: 1-cephalopodic, 2-canine, 3-ursine, 4-feline, 5-evolved birds, 6-completely alien) potentially a lesser species which appears to have been genetically evolved and now thrives in the absence of its creators. They are either indifferent or either outright hostile to the explorers. Indeed, with some time and effort the explorers may win some trust, or may research the ruins independently, only to discover that the surviving graven images of the ancient extinct species look exactly like the Orion explorers! The ancient records, once transcribed by the explorers' AI system reveal that they called themselves humans and the world was called Earth.... 

Mysteries to Solve:

Is the lost civilization evidence that there is a lost age of space exploration among the Orions? Are the Orions descended from these Humans?

Are the current ruling sapient species descended from genetically uplifted animals, or are they the survivors of a species that conquered and defeated Earth?

Is there evidence of extrasolar activity elsewhere in this solar system that can piece together the mystery? Relic space stations in orbit or on the Moon?

Is it possible there is an even greater threat lurking in the darkness of the system, waiting for evidence of visitation, causing the ancient enemy to awaken and respond to the appearance of another spacefaring civlization?