Archaeologists may have found ruins of fabled entrance to Zapotec underworld
Spanish missionaries deemed Lyobaa to be a "back door to hell" and sealed all entrances.

In 1674, a priest named Francisco de Burgoa published his account of visiting the ruins of the Zapotec city of Mitla in what is now Oaxaca in southern Mexico. He described a vast underground temple with four interconnected chambers, the last of which featured a stone door leading into a deep cavern. The Zapotec believed this to be the entrance to the underworld known as Lyobaa ("place of rest"). Burgoa claimed that Spanish missionaries who explored the ruins sealed all entrances to the temple, and local lore has long held that the entrance lies under the main altar of a Catholic church built over the ruins.

An international team of archaeologists recently announced that they found evidence for this fabled underground labyrinth under the ruins—right where the legends said it should be—after conducting scans of the site using ground penetrating radar (GPR), electrical resistivity tomography (ERT), and seismic noise tomography (SNT). The team also found evidence of an earlier construction stage of a palace located in another part of the site.

Mitla is one of the most significant archaeological sites in Oaxaca Valley. It was an important religious center, serving as a sacred burial site—hence its name, which derives from Mictlan ("place of the dead" or "underworld"). The unique structures at Mitla feature impressively intricate mosaics and geometric designs on all the tombs, panels, friezes, and walls, made with small polished stone pieces fitted together without using mortar.

Spanish soldiers and Christian missionaries began arriving in the valley in the 1520s, and several mentioned the ruins of Mitla in their accounts. Naturally, they interpreted the underground temple as a site for an "evil spirit" and its "demoniacal servants." Burgoa's writing is the most descriptive, detailing how the Zapotec high priest used the palace of the living and the dead. He marveled at the mosaics and skilled construction of the site. And he specifically mentioned four chambers above the ground and four chambers below the ground.

A little further in the article it says

A stone slab covered the entrance. "Through this door they threw the bodies of the victims of the great lords and chieftains who had fallen in battle," Burgoa wrote. It seems that certain "zealous prelates" decided to explore the underground structures, carrying lighted torches and using ropes as guides to ensure they didn't get lost. They encountered "putrefaction," foul odors, and "poisonous reptiles," among other horrors.

Then, of course, the Spanish built Catholic churches with the rubble from the site, including right on top of the site. Gotta tear down those buildings, they have no business being there. They did that way too often in villages they conquered.