A house needs human presence; only with life does the house thrive.
A house left uninhabited will "age" very quickly.
In reality, there's no such thing as an aura—it's just that without people living in it, small problems left unchecked can quickly evolve into major issues. It's similar to how weeds and creeping vines, if not dealt with promptly, can aggressively grow roots that damage the structure of a building. These plants also attract insects, which burrow into walls and weaken the structure, leading to an unending cycle of deterioration.
All in all, an underground city so well-preserved likely has one or more guardians to watch over it. Perhaps only some annoying black puddings or green soft mud appear along the way, naturally occurring nuisances.
A massive lion with wings and the head of a female humanoid—a female-faced Sphinx—is one such guardian of this underground city. She's responsible for maintaining the entire structure and protecting it from destruction.
