The article was a revisiting of the life and achievements of the emperor Nero, a bad guy by anyone's measure, but apparently a man with an artistic vision that resulted in an amazing palace, one largely open for the common people to stroll around the grounds.
He built a huge palace that took up a large portion of the Roman city (land available because of the infamous fire that he may or may not have instigated.)
Subsequent emperors appear to have hated Nero so much that they literally buried Nero's palace. One report said some areas were filled with sand, which is why the interior was preserved so well, at least until the fifteenth century.
For fifteenth century artists, it was a popular pilgrimage to be lowered into the cave-like interior of the buried palace to look at the frescoes on the ceilings. Apparently the fill of rubble meant that these early visitors were standing up near the ceiling, and could touch the painted surfaces.
They were so taken with the paintings that they reproduced many of the motifs of these grotesque (i e from a cave or grotto) artworks in their own work. I guess if we did our homework we could figure out where to see them, probably some in the Vatican, I suppose.
The Online Etymology Dictionary writes that this suggested origin of the word grotesque is generally accepted.
Here are a few links that I've just enjoyed looking at.