Ad Daymaniat islands in the Gulf of Oman near the Muscat city are UNESCO World Heritage Site a protected nature reserve. The islands you can reach by boat, a must visit if you are in this region, an excellent place for snorkeling and diving. For example a day trip lasting around 8 hour, from Muscat, is enjoyable between Oct.- Apr. Dont forget the islands do not have restaurants, many tour include snacks, lunch and drinks.
Thanks for your visit have a great day!