Beautiful! There are pristine reefs in the Gulf of Aden near Djibouti. There's a little resort called Sable Blanc, where you can basically walk off the beach with your snorkeling gear into some great reefs. Not too far from there is the lowest point in Africa called Lake Asal, which is one of the saltiest bodies of water on the planet, and is surrounded by an alien landscape. Also you can go during whale shark season and and see those massive animals.