I think many people think of the Amazon rain forest as primeval or virgin territory, untouched by man. This is incorrect. As detailed here on Obsidian Wings, when you look at the rain forest, you should instead think of it as a post-apocalyptic landscape.
While most Americans learn something of the Aztec and Inca empires, I don’t think many quite realize the scope of these civilizations: cities laid out in geometric patterns, roads and bridges connecting them, the cultivation of man-made soil to support a vast population. It is believed that Tenochtitlan was surpassed in size only by Paris, Venice, and Constantinople. So what happened? The Old World met the New World. More precisely, the Old World’s diseases. A host of diseases wiped out 90% of the of the population of civilized Mesoamerica and Andean America by 1568. To compare, the US has just over 300 million people. Imagine if our population was reduced to approximately 30 million people. That’s less than the population of California.
With so many of the people gone, infrastructure collapses as survival becomes essential. Evidence of a “culture” (stories, artworks, crafts) disappears. And nature reclaims the land. It is only within the past 20 years that scientists have been able to determine the specifics of the rain forest’s true past.
This idea of discovering virgin territory is really a post-apocalyptic landscape contains possibilities for science fiction and fantasy stories. What if your space-faring colonists landed on what is thought to be a virgin planet (perhaps it’s seen as humanity’s salvation)? What if they soon discover evidence of one or many civilizations? What if this is humanity’s first contact with an alien species, but they have all long since died? What if whatever killed them (disease or invader?) is still on the planet? What if it ceases to lie dormant?
What if your fantasy story focuses on an age long since passed being rediscovered and influencing the world of your story? What if magic is rediscovered when the post-apocalyptic landscape is recognized for what it is? What if magic was discovered, but the rules (passed down orally) have disappeared? What would experiments with magic look like? What if you were able to compare and contrast modern day with a setting more typical of high fantasy by letting magic slowly seep into the modern day world? Might it be a way for mythical stories to come alive?
Does the Obsidian Wings article change how you look at the Amazon basin? What does it mean if civilizations can disappear from popular memory? How might that affect your story?