After gaining control of the Magic Limb Grafting Worms, Lind had led a swarm of bugs to explore the underground world, and the Soldiers would ride the Catastrophe Warhorses to explore the area to ascertain whether other creatures existed there.
Indeed, they discovered some magical creatures and undeveloped Calamities, especially the emergence of the scavengers which was a pleasant surprise.
Only after Calamities were cultivated was there a chance for a complete Heart of Calamity to appear; regretfully, such "BOSS" level Calamities seldom emerged.
It's likely that there are other entrances to the underground world because the area is too vast to be explored completely in a short time with its endless caves.
