I’ve been to Kauai to train for IM a couple of times. I much referred it to Maui or the Big Island.
Exceptionally scenic long rides from Kapaa/Wailua to the road end past Hanalei or toward Waimea. A long slow run along the Na Pali Coast trail.
Absolutely perfect.
At least it was over a quarter of a century ago.
I have a little more recent data from Kauai… I would say it pretty well sucked for road riding 2004-2006. Beautiful, but dangerous. One main road, lots of traffic distracted or in a hurry, and the shoulder (if there was one) always covered with debris (the road crews would only shove it that far).
I think the safest spot was along the SW side Hanapepe to Kekaha, and the climbs up to Waimea Park. Unfortunately I didn’t live near there.
I’ll put a vote in for Napil Bay on Maui. We stay at Napili Kai annually to enjoy OWS in the bay and great cycling up and around the west end of the island. Plus the wife and kids are safe, sound and content enjoying the beauty that is Napili beach.
Where to stay:
https://www.napilikai.com
http://www.napilishores.com/
What to do:
https://connect.garmin.com/modern/course/14005267
https://connect.garmin.com/modern/course/17092177
https://connect.garmin.com/.../activity/1459911152
Scott