I Hardly know the south side but it’s worth finding a hike you feel comfortable tackling in Waimea if Canyon. It’s a long drive that managed to make 3 out of 4 of us puke.
Also clearly have no idea how to use Bluesky!

There’s a botanical garden with indigenous, endangered plants that’s worth a visit, and I think I remember biking through taro fields…nice to see some of the non-beach, actual living parts of the island.

With the caveat that it’s been 20 years, Kauai is my fav Hawaiian island, north end (without the tour buses!). You can float the Wailua River, then hike up to a waterfall….that was different and lovely. Any hiking along the Na’pali coast (not obscure but v beautiful).