Those who stumble into Dudunsparce holes invariably describe them as 'bottomless pits', quite understandably, as they are far too deep and poorly-lit for anyone to ever actually see the bottom. The pokemon which eventually rescues them is often described as a guardian angel, and indeed the shape of its wings has greatly influenced the depiction of angels; these travelers might not be so grateful, however, had they realized their very rescuer had dug the pit in the first place.
Dudunsparce place their lairs deep within the Earth's surface, and attempt to prevent visitors from falling in, but some do a better job of this than others. Even if a pit is perfectly sealed, however, both human activity and other burrowing pokemon such as Excadrill can reopen the entrance. Stories abound of falling miners or oil workers, together with their heavy equipment, disrupting this pokemon's meals and naps; modern Dudunsparce dig even deeper than their ancestors, to give themselves enough time to catch everyone.
Only Dugtrio go deep enough to visit a Dudunsparce's home without falling, and legends tell of friendship between the two species. What said home looks like remains the subject of immense curiosity, both among pokemon researchers and the general public; illustrators have imagined it as something akin to the Sinnoh Underground, with these pokemon watching fossilization as it happens, or as a mess full of discarded refuse from surface humans and pokemon alike. More sober scientists wonder how any pokemon survives at such a depth, or even finds ground which can be dug through. An attempt to send a Dugtrio as a sort of probe failed because the scientists responsible underestimated the pressures of the deep underground, and the specialized camera imploded; the Dugtrio, by all accounts, still met with a Dudunsparce and had a wonderful time.