premise: It is the best preserved passage tomb in Europe, and is 500 years older than the Pyramids (3000 b.c. ). It's a huge stone mound (nearly 12 m/40 ft high and almost 90 m/300 ft wide) constructed from 200,000 tons of stone, much of which was somehow hauled from the Wicklow Mountains and the Mountains of Mourne.
hypothesis: The tomb is made of grey stone.