"Oh, I'm not surprised! Monsters have been sealed away for a long time... at least where I'm from. But I digress!" After all, this human wishes to know about his world! So this is a good place as any to segue into the glorious realm of the Underground.

...Once he clarifies that detail.

"Well, I'm afraid I can't tell you about the entire world, but I can tell you about a very select part of the world. Namely, the Underground in which all monsters were tragically sealed! It might not be as grand in comparison, but I've grown quite fond of it!" He says, despite having lived there his entire life.