UKH

I have promised my wife a trip to Hawaii next year (November). Her best friend lives in Honolulu and we will at least begin and end the trip with a few days with her.

It will probably be our only trip there as there are many other places I’d like to visit and trips that involve thousands of miles by air are probably not going to feature heavily in our future plans.

With that in mind, what should we be trying to see  whilst we are there?

Volcanic landscapes are worth seeing as so unlike anything else.

I've not been to Hawaii but I heard you can walk through Lava Tubes.

https://www.nps.gov/havo/learn/nature/lava-tubes.htm

https://www.lovebigisland.com/activities-to-do/lava-tubes/ 

Are you only going to Oahu?

Plans are not made yet, beyond the fact that we will be in Honolulu some of the time.

If you’re going to island hop go to Kauai and see the Na Pali coastline by boat or helicopter. 

I would not spend too much time in Honolulu, which is too much like any other big American city. I would suggest getting to Maui, which has an enormous range of activities - every kind of water sport, including surfing, of course; great hiking and walks in tropical rain forests and on the volcano; great food; beaches; sunsets. It's too sweaty for enjoyable rock climbing. Around Lahaina is perhaps the most convenient base on Maui, but it's best to plan your days to avoid driving in the local rush hour traffic.

From Maui, one can make easy day trips to Lanai and Molokai.

The series of ... Revealed guides (e..g Oahu Revealed; Maui Revealed; The Big Island Revealed etc.) are about the best as far as tourists guides go, because they have plenty of general information and advice and not just endless recommendations for hotels and restaurants.

As others have said, my main advice is to look at which islands you want to visit and get to as many as possible.  Oahu is the least interesting island (but still some good things to do).  Worth visiting the classic surfing beaches on Oahu if there is a good swell to watch the surfing.  The round island bus is also good to get an overview of the island.

Make the most of the Japanese food as well.

If I was going to Hawaii I'd make sure a visit to the Keck observatory on Maunakea was at the top of the list but I'm an astrophotographer so I already have an interest. 

The flood defences they're presumably getting ready?

jcm

We went to Oahu 20 years ago as part of a backpacking trip but I doubt it has changed too much since then.

Waikiki is well worth a visit. Excellent shopping (to keep the wife happy!), a lovely beach and nice mellow waves for longboarding if you surf. Also, you can walk up to the top of Diamond Head for spectacular views. The Ala Moana Centre had the widest range of fast food we had ever seen. 

Would recommend visiting the U.S.S. Arizona Memorial at Pearl Harbour, which we found an emotional experience. 

We hired a jeep and camped for free at the stunning Chinaman’s Hat on Windward Oahu. From there, we did day trips to the North Shore to watch the expert surfers riding huge waves at Pipeline and Sunset Beach. There are great waves for bodysurfing (for us mortals!) on the east coast of the island at Makapuu Beach and awesome snorkelling at Hanauma Bay. Check out The Toilet Bowl whilst you are there; it’s an incredible natural feature in the rocks! 

The Lonely Planet guidebook was our bible and had great tips and advice on places to see and things to do, in addition to food, travel and accommodation options. 

I’ve heard great things about Maui too if you have the time to explore other islands.

It’s a wonderful place. Have a great trip! 

I went for a friends wedding in early 2000s. If I remember correctly, we snorkelled with turtles in big island at a cove which was something to do with a King, and did a rib trip to snorkel the submerged Molokini crater. Drove the 'road to Hana' which was Ok if you were the driver but made everyone else seasick.  Go see the volcano where it falls into the sea. If you see signs warning of Portuguese man of war in the sea don't be surprised if you get stung like we did!  I'm a firm believer of making sure I do the unique/special things in a destination, so Hawaii means Volcanoes in that respect.

The car museum in Honolulu is good. They have Magnum PIs Ferrari and strangely for a car museum, the helicopter that seemed to always rescue him. 

Someone upthread says that Oahu is the least interesting island. I've no idea. But it if the swell is up from WNW-NW it might just be worth seeing it coming in as Pipeline onto Ehukai Beach Park on the north shore. For surfers it is one of the best known reef breaks in the world. It is also one of the deadliest. Way bigger than Polzeath.