in James Bonwick's Irish Druids and old Irish religions, in the chapter titled 'sun-worship'. Page 195 in the revised edition states;
"An ancient sculpture in Glendalough represents the long-haired Apollo, or Sun, attended by his doves. These were sun-images in Erin."
An earlier chapter on serpent worship mentions a stone carving of a dog devouring a serpent. Such a carving did exist, George Petrie wrote about it in 1845 saying that it had been stolen in August 1839. He included a drawing of the stone which had been drawn by Gabriel Beranger in 1779. In 1829, local guide Joe Irwin told a visitor that the carving represented St. Kevin’s dog Lupa helping to get rid of the snake which lived in the Lower Lake.
So the book does seem to mention carvings and sculptures that did exist in Glendalough even if the interpretation is not correct. So I'm wondering what the Apollo reference could relate to.