The Portuguese occupiers built the impressive Al Jalali and Al Mirani Fort in the 16th century. Although they're closed to the public, they're a stunning backdrop for stroll along the harbor. The forts are on both sides high on the cliffs guarding the city's entrance.
Visit the Grand Mosque (open in the morning), a gift to the nation from Sultan Qaboos and a mix of Omani, Islamic and modern architecture. It can accommodate 20,000 worshippers and has a rich prayer hall, an elaborate chandelier and a huge Persian carpet that took four years to weave.