recommendations for history and nature/gardens for the other two days:
Foster Botanical Gardens and the Quan Yin temple there
Doris Duke ShangriLa Estate tour
Iolani Place
Bishop Museum

Any particular kind of food? trailandtide's Kaimuki recs are good. If you want to venture a little farther, we had excellent meals last month at The Pig & The Lady in Chinatown (Vietnamese influenced, they started out with a farmer's market booth and also have a brick & mortar location at Ward Village called Piggy Smalls) and Nanzan Giro Giro (Japanese kaiseki, menu changes monthly, excellent value at $58 for 6 courses). We also never miss a visit to House Without a Key at the Halekulani Hotel in Waikiki. It's one of the few places that still has traditional Hawaiian music and hula every night starting at 5:30pm. You can just go for drinks or they have a light dinner menu (food is OK).

Doris Duke estate is definitely a good option
Lyon Arboretum in Manoa is gorgeous ( more impressive than fosters I think)---and free!
Bishop Museum ( for Hawaiian History--- in the past they have had excellent exhibits on the Hokulea and star navigation)
Drive up Tantalus road---its the only historic road in Hawaii---and little known fact---was also bombed during WWII after Pearl Harbor---theres a gorgeous lookout at the state park here called Puu Ualakaa ( best at sunset)---I think you can also arrange to see the Lilistrand House ( historic house by Vladmir Ossipoff)

thanks so much Trailandtide and Patty - we are very open to all sorts of food - we live in a small town without many options so are excited to try cuisines we are not used to.

Loco Moco! Loco Moco!
Spam Musubi
Poke bowls

Not haute cuisine, but unique Hawaii foods!

Quick correction regarding Kaimuki restaurants: Keving Hanney owns 12th Ave Grill and is co-owner of Koko Head Cafe.
Ed Kenny owns Town and Mud Hen Water, as well as Kaimuki Superette and Mahina and Sun's (in Waikiki).

I just returned from 9 beautiful, sunny days in Oahu. I highly recommend the Moana Surfrider. It is steeped in Hawaiin tradition as it was the first hotel in Waikiki. It is famous for the banyan tree in the center of the property and the rocking chairs on the veranda. There are a few drawbacks (smallish pool and you have the pay for beach lounges) but it is centrally located, the rooms are spacious and the staff top-notch.
If the prices are too high, the Sheraton Princess Kaiulani across the street is a nice option. The hotel has been updated and the views from the balconies are amazing. You can watch the 50+ surfers all day, everyday. Our friends stayed there and were very happy. Plus there is a great new show called "Waikiki's Rock'n Reception" at the hotel. We were 8 people and everyone one of us had a ball. It is set in 1955 and is as if you are attending a local Hawaiian wedding reception. There is a yummy buffet, traditional hula dancing, limbo and a great live band. Loved it!
These 2 hotels are also on the same block as the International Mall. A beautiful place with some excellent restaurants. My favorite was Yauatcha Waikikifor dim sum. Don't miss the crispy duck.

Thanks all - we just checked into the Kahala and are finding it lovely and gracious and very comfortable. happy safe travels all