I actually visited Waimea Valley twice. First with Mark, Connie, and Jessica, and then later with Travis and Michelle when they showed up. Waimea Valley is a botanical garden, with a waterfall and swimming pond at the end of the walk.
The site is spectacular. Among the gardens are an archaeological site of a living area for ancient Hawaiians.
The botanical gardens include a large hibiscus collection, along with thousands of other flowers and trees.