"The perfect pet at the perfect price -- guaranteed." Creature Dex at the bottom of the sub, if you want to include "relatively harmless" alien critters in your campaign.
A floating city hovers over the capital, seemingly appearing out of nowhere. Its spires are blinking in the morning sun, revealing alien architecture. What will happen next? Rumours spread like wildfire that this is the ancient city that once stood at this very spot. Mystics proclaim that it will take root here once again, crushing the capital under it. Somebody needs to get up there and investigate.