We stayed in the north side of the Kauai right across from Tunnels Beach for part of ours. The northern trailhead is pretty cool to see, can go as far as your body and experience will allow but at least 30-40min in there's some good spots for pictures of the north side cliffs on the island. Tubing through the old sugar field irrigation. Helicopter ride is a must. Kauai Ono near Princeville is a pretty cool farm to table outdoor dining experience. If you go to the north side past Hanalei and it starts to rain, go back if you're staying on the other side. Once the water reaches a certain point on the bridge to Hanalei they close it. We had flash floods on our trip and basically got stuck there for a few days and no electricity. There's worst places to get stuck but still be warned. Drive and sight see, get out and explore. I could almost do 7-10 days at each island to experience it all.