oahu Audubon National Bird Sanctuary - Google Maps
Aside from the obvious - is there anything "not to be missed" whilst visiting here?
I'm staying in Waikiki
I know this is a few months late but for the record, if you will be staying on Oahu, drive out to the North Shore via H3 driving onto 83, that is where the real Hawaii is at on Oahu. Stay away from the "Polynesian Cultural Center", it's a rip off, it looks cool but it is actually a Mormon operation that has nothing at all to do with Polynesian culture and everything about crazy Mormon shit.
The drive on H3 will take you thru these magnificent tunnels that cut through the mountain range that separates North and South Oahu. On 83, stop at Kahana State Park, it has one of the coolest hidden beaches in Hawaii. As you drive along 83, you will discover it is just one cool beach after another, will little villages where you can dig the local cuisine. My favorite is a little Korean eatry in Kahuku where you can get the best Korean food you ever ate. There are also enumerable shrimp eatries, little grass hut style places - shrimp is the local industry.
Along the way you will run into the Sunset Beach area. Somewhere along there, there is a small volcanic crater at sea level, as the tide comes in and out, it fills with water and then recedes, leaving a crystal clear lake filled with all kinds of tropical fish, you can get right in the water and groove with them. Look for a supermarket with a Starbucks right at the intersection of 83 and some main village road, it's right across the street. The breakers around the outside of the crater are spectacular, and they crash over the rim and form little water falls along the rim as the tide comes in. Make sure you pick up a set of local "reef walker" slippers before you go in the water, under the sand is occasional sharp reef rock. There are also utterly spectacular beaches in that area. Head down the road a little more, to the Waimea Valley Audubon Center in Haleiwa, don't miss it, it is full of Hawaiin natural beauty and a great place to take photos, and if you are into hiking, a number of nature trails have entrances from there. Visit the town of Haleiwa, it is known as the "Surfing Capitol" of Hawaii, it is a cool little town, the Banzai Pipeline Surf Recreation Area is right out front, and the Surf Museum and the freaky people who live there are all a trip, and the town is full of all kinds of little shops you can buy all kinds of local crafts, Hawaiin clothes, surf gear and tourist crap at.
For touristy stuff, there is the whole Pearl Harbor thing. The Arizona Memorial is one of the most emotionally gripping monuments you will ever experience.