This massive structure suffered countless attacks from the likes of Sir Francis Drake in 1595 and the Dutch fleet in 1625. In 1898 American ships fired on it during the Spanish-American War, destroying its lighthouse, which was later restored. Visit hidden passages, aim your camera on the cannons that still guard the harbor, and gaze over the 60-foot tall walls at the ocean. Stroll on the lawns where soldiers once marched and watch the children flying their kites in the afternoon sea breezes. Explore more >>
The hagfish is a slime-emitting ocean-dweller that's remained unchanged for 300 million years--and it shows. It has a skull (but no spine), velvet smooth skin, and a terrifying pit of a mouth that's lined with rows of razor-sharp teeth.