Take a full-day trip from Hoi An and Da Nang to the Cu Lao Cham archipelago, a UNESCO-listed marine biosphere. You'll make the crossing in a traditional wooden boat, then slip into the water to see the bright fish and coral that thrive in the protected area. Following your snorkeling time, head to Bai Chong beach for a Vietnamese seafood lunch at the edge of the water, soaking up the sun on the white sand beach before returning to the mainland.