Waimea Falls, also known as Waihi Falls, is one of the more accessible falls on Oahu. It is located within Waimea Valley, which is a unique Hawaiian botanical garden within a significant cultural and archaeological site. There is a small fee to enter the park. This is a worthwhile contribution, as the place is dedicated to the preservation of the incredible botanical and cultural features of the area. https://www.hawaii-guide.com/oahu/hiking_trails/waimea-falls