This breathtaking cliff-top site on Holy Island boasts walks, a visitor centre and closed circuit TV to view nesting birds. In summer over 4,000 pairs of seabirds nest at South Stack cliffs. From Ellin's Tower visitor centre you can watch puffins, fulmars, guillemots and razorbills, using binoculars and telescopes, and see live pictures of the birds on the cliffs. Superb bird watching opportunities are not the only reason to visit South Stack. The cliffs contain some of the oldest rocks in Wales, dating back nearly 600 million years to a geological period called the Precambrian. The extensive folds in the cliff face bear witness to some of the earth movements and forces that have shaped Wales. The layering of different materials making up the rocks is clearly visible. The sandstone (brown-orange) and mudstone (lighter grey) layers have acted differently as they've been folded