On the Indian Ocean just south of Malindi, Watamu is somewhat less touristy than other beach areas. It's a good place to relax and snorkel. Watamu Marine National Park has coral reefs and underwater caves, so the scuba diving is good (and equipment can be rented at reasonable prices).
You can also swim with dolphins in the park. If you don't want to get in the water, you can see the reef from a glass-bottomed boat. There is also an interesting and worthwhile turtle-conservation project in the village to protect the turtles that nest on the beach. Nearby are the 13th-century Gedi ruins, which have been restored and include tombs, a great mosque and a palace—they're best seen in the afternoon.
70 mi/115 km north of Mombasa.