The western region of Kauai offers some phenomenal hiking trails, some of the best you'll find anywhere in Hawaii!
If you're looking for an excellent full-day hike, with great views of the Na Pali coastline, then be sure to hike down Nualolo Trail, take the Nualolo Cliff trail to Awa'awapuhi, and hike back up the ridge to where you started.
If you are looking for in-land views of the Alakai, then the Alakai Swamp and Pihea Trails are for you. For an excellent half-day to full-day hike, take Pihea to Alakai junction, and then take Alakai to the end where the lookout, when the weather is clear, offers a breathtaking view (you can see to Hanalei Bay).
The Cliff, Canyon, and Kukui Trails also are the three best trails in-land for Waimea Canyon.