The wrinkled sea (line 4)
If you've ever seen the ocean from an airplane – about a thousand feet up – you know what a "wrinkled sea" looks like. The eagle doesn't exactly "explore" the ocean, but he explores a different perspective on the ocean.
he falls (line 6)
At the end of the poem, the explorer returns to our world. Like a whale surfacing to take a breath, the eagle comes back to earth.