He urged on his horse then, and came up to the mound,
there lightly alit, and lashed to a tree
his reins, with a rough branch rightly secured them.
Then he went to the barrow and about it he walked,
debating in his mind what might the thing be.
It had a hole at the end and at either side,
and with grass in green patches was grown all over,
and was all hollow within: nought but an old cavern,
or a cleft in an old crag; he could not it name
          aright.
          'Can this be the Chapel Green,
          O Lord?' said the gentle knight.
          'Here the Devil might say, I ween,
          his matins about midnight!'

SIR GAWAIN AND THE GREEN KNIGHT
(Translated from Middle-English by J. R. R. TOLKIEN)