The Depths, a network of interconnecting tunnels, ancient ruins, and caverns
worn out of the rock, rests underneath the Kingdom of Terranotos. It was
originally discovered fifty years ago by various farmers and miners about
simultaneously, but none of them knew what they had really found. At the time,
children were allowed to play in the Depths, as long as they didn't stray too
far from the light.
About 40 years ago, it was figured out that these caves were the source of the
dangerous creatures that had been popping up for the past three-fourths of a
century. Mercs suddenly became much more prosperous and prevalent, hired by
citizens to go into local enterances to exterminate any monsters they came
across. The deeper these Mercs went, the fewer of 'em came back alive.
As these Mercs and Wanderers explored the caves and ruins, however, they found
records of previous explorers, who detailed various items they had found in the
Depths - mythril blades, maps to treasure, everything a Merc dreams of. So some
stopped taking jobs from the citizens of Terranotos and went into the business
of "delving the Depths" for the sake of the treasure they might find.
Several of these fellows got rich off of this.
Many, many more followed the legends of these delvers.
Now, an entire industry has sprung up around exploring the massive network
underneath the Kingdom, supplying everything from candles to rope to guides and
experts. This new industry of finding and exporting (some) of the riches found
underground has turned Terranotos into one of the most influential nations
today.