Forgotten Realms Underdark
"Absence of light results in darkness. So, what results from the absence of Good? The Underdark is a place with very little of either. ” — Mordenkainen
Forgotten Realms is a fantasy world setting, described as a world of strange lands, dangerous creatures, and mighty deities, where magic and supernatural phenomena are quite real. The premise is that, long ago, planet Earth and the world of the Forgotten Realms were more closely connected. As time passed, the inhabitants of Earth had mostly forgotten about the existence of that other world – hence the name Forgotten Realms. "Herein lie the lost lands"
The Underdark is the vast network of underground caverns and tunnels underneath the surface of Abeir-Toril. It is home to a host of evil beings driven deep into the caverns at the end of the age of demons.