The tiny dwellings, taller than me but shorter than Merlin, were in excellent condition and - unlike the archway we first discovered - were free from litter accumulation.
Inside was cool and moist feeling and the stonework was simply amazing.
Light came through the top, the point of the cone, and illuminated just how precisely and skillfully the thin smooth stones had been piled up. After a quick google of "cone shaped stone dwellings near Castel del Monte," I found out that the structures were trulli (conical stone dwellings specifically found in the Puglia region of Italy). Communities built them without any mortar or cement so that they could be dismantled if a taxation inspector was coming to their village. It was their way of dodging any fees for owning property.
I also found out that the specific field of them we'd stumbled upon is for sale. Apparently, buying trulli real estate is a new craze amongst English and German tourists. At least according to Wikipedia and Lonely Planet.
Trulli usually date back to around the 15th century, something that initially disappointed us. Due especially to their diminutive size, we assumed they were more ancient. It's amazing how much Italy will spoil you on something actually seeming old.