Marsa Mubarak is the most rewarding easy excursion from Port Ghalib. The bay has reef, seagrass, turtles, and sometimes dugongs, which makes it unusually good for snorkellers as well as divers.
Choose a trip that keeps distance from wildlife and does not chase animals around the bay. The best experience is slow and quiet: floating over the seagrass and letting the turtles appear on their own schedule.