Re: Hawaii
Kauai is largely unfucked by humans, making it the best natural wonder of all the Hawaiian islands if you're willing to put some effort into seeking its treasures. They call it "the garden isle" for a reason. You could probably crack into some of it with a day trip, but better with a couple of days to get deeper into it.
Can you go island hopping for a day? Depending on the flights, you could make a day trip out of it, but it would be worth your while to at least stay one night and get two long days out of Kauai. Most of the treks we went on take an entire day, and it would suck to have a flight looming at the end of that day.
Some highlights on Kauai:
Polihale State Park is as far as you can go on the western side of the island by vehicle, and it's worth it.
[URL="https://www.google.com/search?q=polihale+state+park&biw=1293&bih=721&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj775Pku7vLAhWI7yYKHSa4DYgQ_AUIBygC"]polihale state park - Google Search[/URL]
You'll have to google directions, and rent a jeep to get there. If there have been any significant rains, you'll need the 4x4. If the sun is shining you'll enjoy the top down (the jeep.) I didn't see one human once we passed the old naval missile site, polihale is another hour or so past that. You can camp anywhere on the beach if you're up for it.
Nearly all of the Kauai is a state park, and you're free to trek most of it as you wish to your abilities. Waimea Canyon, Wailua River, Hanalei bay area, etc.
Highly recommend renting a kayak on Wailua river. There is a small marina near where the Wailua meets the ocean- from there it's about a 45-60 minute row up river to the Secret Falls hike point. Dock your kayak and hike about 1-1.5 hours to the falls. It's an easy hike. If you're old enough, you probably remember the opening scene from Fantasy Island with Herve Villechaize, that was shot at the Secret Falls. The only way to get to this spot is hike or see it from the air via helicopter. You can take a guided tour if you're less adventurous, but you're going to be with 20+ other touring schmucks with cameras ruining every shot you try to take, or complaining about their kayak, or bitching about the hike. Worst of all you move at the groups pace, not your own. Nature is best observed through your own personal space with a companion or few.
Pro tip- Group tours fucking suck, everywhere, all the time- avoid them at all costs everywhere you travel- you can see most of the same stuff on your own with some effort and your experience will be worlds better.
Jurassic Park was filmed on Kauai, and the opening gates to the dinosaur park are still standing, though the rest of the set has been retaken by nature. The only way to see this is via jeep, a map, and a compass. Google it. Worth it.
If all of that sounds like too much for a quick jaunt to the island, just renting a jeep, taking the top down and cruising the coast line through the various small coastal towns as you round the island it also worth it and super easy to do. You can drive to the top of Waimea Canyon, and it's pretty spectacular to see if you haven't seen the Grand Canyon, nothing compares to some of those vistas, tho some of the shit I just saw in New Zealand certainly ranks up there.
Anyway, Kauai. Go. You won't regret it.