Pu’u Manamana is an absolutely incredible hike that’s not for the faint of heart. At times you will be standing on the top of a ridge that is a foot wide with steep, hundreds-of-feet drop-offs on both sides. You need a clear day with no winds for this one!
Kayaking to and hiking Chinaman’s Hat is one of my favorite things to do on Oahu. To get to the island you can kayak, paddleboard, swim, or paddle through relatively shallow and usually super clear water. During low tide you may even be able to walk all the way to the island!