I don't recall hearing the guide say this in 2001, but read today that:
"Quite the most impressive feature of the tomb is the fact that the side walls, roof and floor of the passageway consist of four single slabs, each approximately twenty feet long. The transport and erection of such stones would cause problems for the heaviest modern engineering equipment."
(Quote from: 'Circles & Standing Stones' by Evan Hadingham, 1978 edition, charity shop bargain!)
Something is not right. This message is just to keep things from messing up down the road