Complex sentence: The Cape's importance declined with the opening of the Corinth Canal which allowed ships to by-pass the Peloponnese rather than circumnavigate it, however, at present times it still has significant amounts of sea-traffic.
Split into simpler sentences: The Cape's importance declined with the opening of the Corinth Canal, which allowed ships to bypass the Peloponnese rather than circumnavigating it. However, it still has significant amounts of sea-traffic.