Complex sentence: Studying the waters around the island, Papillon discovered a rocky inlet surrounded by a high cliff where he noticed that every seventh wave would be large enough to carry something on the water far enough out into the sea to drift towards the mainland.
Split into simpler sentences: Studying the waters around the island, Papillon discovered a rocky inlet surrounded by a high cliff that caused a phenomenon to occur in the water currents. He realized that every seventh wave would be large enough to carry something on the water far enough out into the sea to drift towards the mainland.