A discussion about a possible origin of the engravings at Newgrange Mound is given. The engravings are one of the most famous megalithic tombs in Ireland that could be evidence of ‘pinhole optics’ used for solar observations. Also, they could represent an early manifestation of the construction of a specially oriented astronomical instrument in ancient times. Newgrange’s inside chamber dimensions (orientation, depth and height) are analysed to give support to the hypothesis that the figures in the east recess at the ‘roof stone’ were made following the images produced by an array of pinholes. The instrument, we suggest, was located at several positions along the passage before it was covered by the mound; the images inspiring the engravings were observed on the day of the winter solstice at sunrise around 5000 years ago. The evidence reported here could help to relate other engravings and figures to the use of ‘pinhole optics’ by other cultures.