The Kilauea Lighthouse is a place you almost certainly scene before coming to Kauai. It's one of her signature images. It's a few dollars to get into the lighthouse area but there is a fine lookout just before you hit the parking area if you wanna be super careful with your money. This area is also a bird sanctuary and you'll see giant white birds flying all over the place.
As you near the end of the road past Hanalei, you'll come across a giant cave just to the left of the road. Park across the street and give it a look. It's called the dry cave. Tunnels Beach is outstanding too with breathtaking scenery and good snorkeling during the summer. By the way, Tunnels gets its name for the wide network of reef tunnels off shore. You have to scuba dive to see them.
Known locally as Waiʻoli Huiʻia Church. This historic Christian church in the American gothic style with a tower housing is located right of the road just past the main area of Hanalei Town. The church itself would be impressive anywhere but when you put one of the iconic mountains in Polynesia in the backround, well, let's just say you at least need to get out of your and take a picture.
This is an awesome botanical garden. It's ground are on the site of an ancient kauai village whose remains you can still see today. Limahuki has even restored some of the ancient aquaducts Hawaiian used for their crops. This place is just a great blend of raw untamed jungle and educational exhibits.