Līhuʻe
Float through five 19th-century sugarcane plantation irrigation tunnels — pitch-black passages illuminated by your headlamp. Originally built in 1870. Ends at a natural swimming hole. The only activity like it in Hawaii. A perfect counterpoint to beach days.
Book at kauaibackcountry.com; from $125/person. Maximum 12 guests per tour. Book 2–3 weeks ahead. Minimum age 5, weight limit 300 lbs.
Tunnels are indoors — ideal rainy-day activity unaffected by weather.