I have a little bit of time this morning to come back to this. As I mentioned, most of my knowledge is about Kauai and Oahu. Although, I do know the answer to
@Malamute's question from above. The volcano is Haleakala on Maui. Summit is just a touch over 10,000' and yes, it occasionally snows. There is a crater hike as well as an astronomical observatory. I know people that have gone up there, skied part way down, switched to mountain bikes then switched to surfboards. It'd be pretty cool to hit my 3 favorite sports all in one run.
Anyway, here's what I know. This might get a little wordy.
In general, I've always treated Hawaii like any of the other South Pacific islands (Fiji, Samoa, etc) I have visited. You are the foreigner. Yes, it is a US state but that doesn't matter. Culture there runs deep. Respect it and the people. Try not to act like a tourist. Do not leave anything of value in your rental car. Especially if you pull up and park at someplace like Sandy's or Makaha. Leave the windows down and the doors unlocked. There are still many places where haoles are not welcome. Respect that as well.
On Oahu...
Traffic sucks. Honolulu is just like LA. If possible, stay off the H1, H2 and H3. You can get around the island just fine without using the "interstates". You're on island time anyway. Relax and enjoy the slower pace.
There are a few things worth taking a look at in Honolulu proper. Obviously, Pearl Harbor and the Arizona Memorial. This should be at the top of your list. It's history and it's important. The Arizona is a powerful place.
Chinatown. This is amazing. Authentic restaurants with some of the best dim sum I can ever remember having. If you're into markets (I am and tend to seek these out on purpose), you will makes some amazing finds. The markets are traditional and you will be hard pressed to hear English. Sights and smells will put you right into Hong Kong.
The Iolani Palace and King Kamehameha statue are worth taking a peek at as well.
Starting to move out of Honolulu. Diamond Head is worth a quick hike. Views are great. If you've got kids, and you're visiting in the winter, Kailua Beach Park is worth a visit. There will be no surf here and the beach is expansive.
Next history stop would be the B'yodo-In Temple. There is an extensive all Japanese cemetery as well as the 18' tall carved Buddha.
One of the most amazing hikes I've done is the Haiku Stairs or Stairway to Heaven. Unfortunately, I believe it is now off limits. It's worth looking up for the pictures alone.
From the Temple, you can head north up the 83 along the coast. On the NE corner of the island is the James Campbell National Wildlife Refuge. It's worth a look. Once you pass that, close your eyes until you get past the Turtle Bay Resort. You can open them again when you hit Sunset. If the surf is firing, stay here and watch for a bit. Next stop is Ehukai Park, Pipeline. If you've never seen the power of South Pacific surf, stay awhile.
Pipeline has 3 reefs. In the summer, there is great snorkeling. In the winter, feats of amazing physical ability. On big days, 7-10' Hawaiian (14-20' everywhere else), the waves will be breaking on the 2nd and 3rd reefs. It is a massive amount of water and it moves like no other wave I've ever seen. It is scary fast.
Next to Pipe is Backdoor which is the right to Pipe's left. Very similar wave just going the other direction. After that you can mosey down the beach all the way to Keiki and Shark's Cove. If you don't want to walk in the sand, there is a bike/walking path that runs in between the houses and the highway.
As I mentioned earlier, Keiki is where we always stayed. The beach out front is peaceful and they've strung hammocks up in the trees. The surf there can be just as large and violent as the big surf spots down the beach. However, where Pipe breaks in 8-10' of water, Keiki breaks in 4-6. It is unforgiving and the realm of body surfers and body boarders. Here's an idea.
Once you pass Shark's Cove, you get to Waimea Bay. Again, just mind blowing surf in the winter if the swell direction is right but also a great spot to just kick it in the sand. Across the street from the Bay is the
Waimea Valley Gardens. Great spot to take a relaxing stroll. Except for the peacocks. They can be a touch on the aggressive side. It also has the potential to be a little muggy and buggy so bring the bug spray.
After Waimea is Hale'iwa. This is a little tourist spot but the
shaved ice is welcome on a warm day.
Through Hale'iwa, you'll end up driving out to Kaena Point. There is some hiking out here along with a bunch of military stuff. You will also see quite a few tent towns. I had heard rumblings that the state was trying to force them to other areas but I do not know the outcomes. Most of them are squatter families.
Kaena Point is the end of the road. To get to the west side of the island, you'll have to backtrack to Kam Hwy and head south over the hill to the H2 into Honolulu. From there, get on the H1 and head over to Makaha and the end of the road on the south side of Kaena Point. This is the empty side of the island. Far more localized. If you are asked/told to move on, nod your head and apologize for the intrusion.
Kauai will be in the next post.