Snorkeler's will find that the waters in Hawaii are particularly clear and that much of the fish life is endemic to Hawaii. Popular snorkel spots include Hanauama Bay on Oahu, Molokini Crater just off of Maui, Kealakekua Bay on the Big Island and Anini Beach County Park in Kauai.
Go Whale Watching
If you enjoy wildlife, one of the most majestic sights you can see is a humpback whale breaching. Between the months of December to April this is not an uncommon sight in Hawaii, where the whales come every season to give birth and to breed. Consider taking a whale watching boat tour to get closer to these behemoth creatures or simply look for a high overlook facing the water and watch from shore.
See an Active Volcano
Visitors to the Big Island should not miss a trip to Volcanoes National Park where you can see active volcanoes. You can either take a helicopter tour above the volcano or hike to the lava flow and watch as it flows into the ocean. The flow changes from day to day so be sure to check the National Park Service website for the most current information.
Take a Helicopter Tour
One of the best ways to truly appreciate the landscape of Hawaii with its volcanic craters is to see it by air. In particular, visitors to Kauai should not miss a helicopter tour of the island's Na Pali coast. Since much of Kauai is inaccessible by road, this is an excellent way to see the island.
Another fun way to spend time on the water in Hawaii is to rent a kayak. There are numerous kayak rental companies all over the islands which will outfit you with everything you need to go kayaking. Some of the best places to go paddling around Hawaii are at Kealakekua Bay on the Big Island, kayaking to the offshore islands around Kailua Bay on Oahu and around Olowalu in Maui. One of the few ways to access the Na Pali coast on Kauai is by kayaking, however this trip takes several days.
Visit the Arizona Memorial
Visitors to Oahu should stop by the Arizona Memorial. The memorial is accessible by boat, and sits above the site where the USS Arizona sank during the Japanese attack on Pearl Harbor. According to the National Park Service, to this day, more than 1100 bodies are still interned there. Tickets to the memorial are free but lines for it can be long. Whilst at the memorial consider stopping by the nearby Pacific Aviation Museum, USS Bowfin and the USS Missouri.