If this is your first time to Hawaii, or you have vacationed in Hawaii before but never left Waikiki, then this itinerary is a great way to explore things to do in Oahu and get a better feel for the island as a whole. Note that below is only a suggestion. Feel free to tailor this itinerary to your needs whether it is doing the days in a different order, leaving things out, or adding things in. Check out the Go Oahu Card for discounted entry to Oahu attractions.
Day 1 - Waikiki (Where Else!)
Why not start your trip off with the beach that makes Oahu famous - Waikiki Beach. Grab your towel, sunscreen, and plenty of water and head to that white sand oasis. When it gets too hot, wade into that crystal blue water that is Waikiki. There are plenty of opportunities to learn to surf or paddle board. Once you have had your fill of sun and sand, take a walking tour of the area. Walk down 'the strip' also known as Kalakaua Avenue. Don't be afraid to turn off Kalakaua, away from the beach towards Kuhio Ave.
It is very difficult to get lost in Waikiki as long as you know which direction the beach is, so explore away! It helps that Waikiki is very pedestrian friendly. The hotels, shops, and restaurants in Waikiki are all stacked within a small radius two miles long by five (or so) blocks wide, bordered by the Ala Wai Canal and the white sand of Waikiki. Be sure to wander into the International Marketplace located across from the Royal Hawaiian Shopping Center. At International Marketplace you will find countless souvenirs' shops and local style foods. Vendors will vie for your attention with 'pick a pearl' displays and well aligned kiosks. There is often free Hula Shows at night near the food court within the International Marketplace.
Day 2 - North Shore with Haleiwa and Sunset Beach
Waikiki is amazing, but there is so much more to Oahu than this pristine beachfront. Rent a car and cruise North to Haliewa (pronounced Holly-evuh). You can also opt for public transportation, but it will likely take you nearly two hours (rather than 45 minutes) to get to your destination. On your way try stopping by the Dole Pineapple Plantation and learn how long it really takes to grow a pineapple (Opt for Kamehameha Hwy North rather than State Hwy 803). You can tour the Pineapple Plantation grounds for free, but it will cost you a few bucks to ride the train or navigate your way through the world's largest maze.
Continue North of Kamehameha Hwy and follow the signs to the historic town of Haleiwa. Unlike Honolulu, parking here is typically free. I recommend parking at the North Shore Marketplace. From there you can tour several galleries featuring beach art and amazing photography of Oahu beaches and ocean life. There is a glass blowing studio where you can watch the delicate art in progress. Around the corner to the left is Ron Artis' surfboard studio. He uses old surfboards as his canvas - definitely worth a look. While here you can beat the heat with some delicious Hawaiian shaved ice. There are several shops along the way that serve this delicious Island treat. Of course, your trip to the North Shore would not be complete without visiting a local shrimp truck. These trucks can be found throughout the island of Oahu, but are especially abundant on the North Shore where they have access to very fresh, and tasty shrimp.
Once you have felt the essence of Haleiwa, continue North on Kamehameha Hwy towards the ocean. When you hit a fork in the road, stay to the right (Kamehameha Hwy) and the ocean should be on your left. As you drive the North Shore you will see beautiful beach after beautiful beach. Feel free to stop by any beach that catches your eye, but the beach we seek is the infamous Sunset Beach. Bone shattering waves crash onto the shores of Sunset Beach during the winter time, creating a haven for surfers. Swimming is not recommended due to the extreme shore break and strong current. The purpose of this beach is to watch locals surf (and get a tan). As a side note, a great snorkeling spot where you can usually find green sea turtles is Shark's Cove, situated just two miles south of Sunset Beach, across from Foodland and Pupukea Road. Stay clear when the surf is too rough (December through February). The rest of the year, the cove is usually calm enough for a great snorkeling experience as it is protected by an outcrop of rocks.
Day 3 Hanauma Bay, Coastal Drive, and Pali Lookout
Hanauma Bay is to snorkeling what Waikiki is to beaches. This protected crescent shaped cove is actually a nature preserve that educates snorkelers while providing a haven to local fish and coral. It is best to visit in the morning before 9:30am or early afternoon when the morning snorkelers have cleared out as the parking lot closes when it reaches capacity. Before entering Hanauma Bay it is required to watch a quick video that details the history of the Bay, points out some of the fish you may find here, and outlines the rules of the Bay. The best parts to snorkel are either the far left or the far right where the water is deeper and the coral has created mini coves. Hanauma Bay parking $1.00 and admission is $7.50. Closed on Tuesdays.
From the gate of Hanauma Bay turn right onto Hwy 72 East to continue onto a beautiful coastal drive of Oahu's south shore. The winding road offers views of the ocean below and volcanic outcrops on the left. There are plenty of scenic lookouts along the way, the most notable is Halona Blow hole. These are great places to pull over, get some pictures, and allow for the driver to really take in the sights as well. Continue on Hwy 72 East and you will pass some local beaches including Sandy's and Makapuu. I would recommend bypassing those beaches due to the strong shore breaks and continuing to Waimanalo Beach Park (if you feel like more sun and sand).
If there is still daylight out, continue on Hwy 72 East until you see the signs for Hwy 61 (the Pali Hwy). Follow the signs to get onto Hwy 61 South. This is the Pali Highway and is literally carved into the mountains. About halfway up is the Pali Lookout. There is a sign that says scenic lookout - follow it! The sign will lead you up a winding road to the Pali Lookout which will greet you with sweeping views of Oahu's South Shore. It will be windy and cooler at this elevation, but if you didn't bring a jacket or sweatshirt you can survive a few minutes in your beach-wear. If the wind hasn't swept you away, you can continue South on the Pali towards Honolulu. You have basically driven a big circle of the Southeast shore of Oahu as the Pali will take you back to Honolulu-Waikiki area (there are ample signs along the way).
Day 4 Historic Honolulu and Chinatown
Hawaii is the only state in the US where you can find a Royal Palace, and the Iolani Palace in Honolulu is a must-see. Guided tours are highly recommended to truly appreciate the history of the Palace as the docents do a great job of bringing history alive. If not a guided tour, at least opt for a self tour with audio because although the Iolani Palace is gorgeous to look at, it is the history behind it that is truly inspiring. At the Iolani Barracks where you purchase tickets for the Palace tours/entrance, there is a great pamphlet that has a map of all the historic buildings within walking distance of the Palace. Be sure to grab one for after your tour!
Just a few blocks North from the Iolani Palace is Honolulu's Historic Chinatown, a triangle shaped area bordered by Beretania and King St. There are tons of shops and scrumptious bakeries aligning these streets. Feel free to pop in and out of a shop that catches your attention. You can find great deals on cooking sauces, noodles, and exotic produce. Or you can stop into one of the many restaurants to enjoy some authentic Asian cuisine.