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.
And of course, at the end of the trail is the waterfall. Somewhat lame is that they require everyone to wear a lifevest, and there are quite a few people.