The hike is about 11 miles one way. We made it a two-night, three-day trip. The first day started at about 9am. We parked the car at trailhead. We heard that there were break-ins in the past. Luckily it did not happen to us. We were also lucky to take the last parking spot in the lot. Good parking spots are limited. So try to get there early. It took us about 6 hours to get to the Kalalau beach including rests, lunch and taking photos. In my opinion, the challenge of this trail is the heat. We sweat a lot. It would be better to start as early as you can. The trail is very well maintained. The famous Crawler's Ledge at 7 miles was actually not hard at all. As long as you move stably you will be fine. If it rains, however, the entire trail can be muddy and dangerous. Although I saw people hiked without trekking poles, for me, trekking poles are must-have.
Besides regular hiking gears, a very important item you want to take is swimming suits. At the beach there is a waterfall. You can take shower there. You will also need a bucket to carry waters to your campsite. For sleeping gears, full sleeping bags are definitely overkill. We carried long underwear, sleeping bag liners and a flat down quilt. What I found was with long underwear and liner alone I felt a little cold (65F) at night; the long underwear and a down quilt shared with my wife provided right amount of warmth. We also got a lot of bites by either mosquitoes or flies. So some repellents would be helpful.
Kalalau Valley Big Pool.gpx and Mokolea Pool.gpx from my GPS Tracks Collection.
Honopu Ridge Trail (around 4 miles round trip). Although many places mentioned this was a hunter trail and was not very well maintained, at the time we hiked it, we found it was maintained well. At intersections, you can always find pink ribbons that help you to navigate. We never got lost even once. I recommend you to wear long pants. There are sections with stiff fern branches that can scratch your skin. A pair of good hiking shoes are also recommended. At the end of the trail, you basically walk along the knife edge of the vertical cliffs. Don't be shy to stop when your heart cannot take it because a single mis-step can cause one's life. The view is absolutely stunning, which makes entire adventure total worth it.
Pihea Trail to Alaka'i Swamp Trail (around 8 miles round trip). This is an interesting trail. You will appreciate the miles and miles of boardwalk. The end of the trail is Kilohana Lookout. At the time we hiked it, it was extremely foggy at the lookout. Because of this, we was not able to see anything. The boardwalk itself made the trip worth the effort.
Hanalei 'Okolehao Trail (around 4 miles round trip). This trail offers pleasant view of north side of the island. The mountains are green and lovely.

Sunset at Kalalau Trail | The photo was taken on a small hill a little north at the intersection that goes into Kalalau Valley.

Rainbow at Lolo Vista

View from Nu'alolo Cliff Trail

Awa'awapuhi Lookout

Sunrise at Pu'u Hinahina Lookout

View from Honopu Trail

Sunset at Hanalei Valley Overlook

Sunrise at Hanalei Bay Pier

Sunrise at Hanalei Bay Pier

Sunrise at Pools of Mokolea

Hanalei Bay Pier

Sunset at Queen's Bath

Sunset at Queen's Bath

Sunset at Queen's Bath

View from Hotel Room in Hanalei Bay Resort

View from Hanalei 'Okolehao Trail

Sunset at Secret Lava Pool

Sunset at Hanalei Valley Overlook

On Kalalau Trail

Sunset at Kalalau Trail | The photo was taken on a small hill a little north at the intersection that goes into Kalalau Valley.

Waimea Canyon Picnic Area Late Afternoon

Sunrise at Shipwreck Beach

Sunrise at Shipwreck Beach

Waimea Canyon Lookout

Pu'u o Kila Lookout|Late afternoon.

Sunrise at Waimea Canyon Lookout

Waimea Canyon Lookout

Sunset at Canyon Trail

Sunrise at Pu'u o Kila Lookout