Get dirty chasing waterfalls
The best part about a post-rainy day is rainbows, but the second-best thing? Waterfalls. After a moderate-to-big rain, slather on the mosquito repellent and head to the gorgeous Manoa Falls, where the trail is short, the forest is green, and the waterfall is an amazing 150 feet tall.
Hike for a sunrise view
Set the alarm, bring your hiking shoes and a flashlight, and trek up the steep path up the Kaiwa Ridge Trail to the Lanikai Pillboxes, where you can perch and see the sky transform from black to purple to blue. It's free, of course, and staggeringly pretty if you can get there early enough.
Challenge each other to a day of indoor climbing
Of course, Oahu’s mountains means outdoor hiking options abound, but if you’re looking for an indoor alternative or rainy day activity, the Arch Project Climbing Center gives you 2,000 square feet of terrain to explore without layering sunscreen and mosquito repellent. Full day passes are just $18.