I found an old Wolfe Tones program from their 25th Anniversary tour and it lists the words for many of their songs including "Newgrange", so here you go.

Your mysteries lay hidden in stones that can't speak,
Thru' time all your wondrous knowledge we seek,
Be ye tomb or a temple we'd like to know why
On mid-winter's morning you seek light from the sky,
Your white quartz stones must have brightened the days
When the sun it shone down and reflected its rays,
You refuse us a key or some Rosetta Stone,
We gaze on just Circles and Motifs and Bone.

chorus:

Sing away Bru/ na Bo/inne on the Banks of the Boyne,
Fal de da for your glory would not yield to time,
Glory o! to the men and the women laid to rest
Who brought greatness to Ireland, the Isle of the Blessed.

From your pillars of grandeur and the answer is sought,
When the tombs of the Pharoahs were only a thought,
Irish folk in their labour looked up from the Boyne
To see standing a temple that would not yield to time.
You saw Cheftains, Na Fianna and monks stopped to call
And they trampled the hills onto Tara's Royal Halls,
And they watched on the Cradle of our art and design
That inspired Irish artists much later in time.

Chorus:

For you're set in a county still Royal with its arms
With a river of beauty with countless wild charms.
You stand there majestic and tower on the plain,
And your Passage of Wonder a secret remains.
So be proud all of Ireland of a history long gone,
That inspired generations of men later on.
Your age is your greatness and a testament still
As we look at Bru/ na Bo/inne on a Co. Meath hill

Chorus:

All the best,

Mick