Dedicate the fourth day to exploring the vibrant underwater world of Hundred Islands National Park. Grab your snorkeling gear and dive into the clear waters teeming with marine life. Discover colorful coral reefs, tropical fish, and other fascinating creatures. You can rent a kayak or hire a boat with a glass-bottom to explore the different snorkeling spots around the islands. Don't forget to bring an underwater camera to capture the beauty of the underwater world. After a day of snorkeling, relax on the beach and enjoy a beachside barbecue dinner.