Complex sentence: The other main way around South America was by way of Drake Passage, south of Cape Horn--the body of water between the southern tip of South America at Cape Horn, Chile and the South Shetland Islands of Antarctica.
Split into simpler sentences: The other main way around South America was by way of Drake Passage south of Cape Horn. It is the body of water between the southern tip of South America at Cape Horn, Chile and the South Shetland Islands of Antarctica.