Answer:
This sparkling globe can float on water. It is light as a feather, but ten giants can't pick it up.
I occur twice in eternity. And I'm always within sight.
What instrument can you hear but never see?
My second is performed by my first, and it is thought a thief by the marks of my whole might be caught.
Ancient and majestic, great big piles of stones, Used to encase both riches and bones. Seen from certain angles, They look like big triangles.
I run through hills. I veer around mountains. I leap over rivers. And crawl through the forests. Step out your door to find me.