Oahu a.k.a. "The Gathering Place" is the most populous Hawaiian island and home to famous Waikiki and Pearl Harbor, the opening battle of World War II. The island measures just 44 miles long by 30 miles wide. If you hear people talking about the "North Shore," they're talking about Oahu - during winter months the waves get massive and this becomes a prime surfing spot. Diamond Head is a volcanic crater that's also a popular hiking spot with excellent views. Hanauma Bay is close by and renowned for spectacular snorkeling. Although it can get crowded, you will see many amazing fish.