Glass Beach is often overlooked and unheard for a few various reason, but is great for capturing waves against the unique lava bed formations on the South side of the island.
The shoreline of Glass Beach is covered with millions of brown, aqua, clear and blue sea glass pebbles, but also consists of other remnants from what looks to be a former salvage yard (do not walk barefoot in this area). Although that may be the case, there is a lot of beauty to be captured here, and it is often drier than other parts of the islands which is ideal for capturing a sunset.
This beach is located in the industrial part of Kauai near Hanapepe Bay. Once you get to the dirt road, you can either walk the short distance or drive it if you have a high clearance vehicle. You will eventually make your way down to the lava pools and other various formations, which are great to capture as the waves come crashing in. The natural bridge was a personal favorite and is a great place to capture a long exposure photo. There is definitely a lot to explore so get there a little in advance of sunset to scope out a few spots beforehand.