In the center of New England only very few and small natural caves exist, but there are numerous artificial caves made of huge slabs of the typical local rocks, especially granite, probably built because of the lack of natural caves. The question is: when they were built, by whom and what for?

Upton Chamber, Mystery Hill, Calendar I, Calendar II, and Druid's Hill are the names of some of the 300 artificial rock constructions. They resemble Celtic remains from the British Isles like Stonehenge or Newgrange, this places have an ancient touch, though there is no evidence that would date them.

Upton Chamber is one among the largest and most perfectly built stone chambers in New England at 3.65m in diameter and 3.35m high. It was constructed in a hill. The walls are made of small, quarried stones, topped by a ceiling of several oval stones weighing several tons each.