Mt. Washington via Ammonoosuc Ravine Trail and Jewell Trail at the White Mountain National Forest in New Hampshire is a difficult 9.7-mile loop to the summit of Mt. Washington and a stop by both Lakes of the Clouds.
Trails: This hike encompasses the Ammonoosuc Ravine Trail to Lake of the Clouds hut, continues on to the Mt. Washington summit from the Lake of the Clouds hut via Camel Trail to Davis Path to Crawford Path. The hike finally heads back from the summit via the Gulfside Trail which leads to the Jewell Trail and down to parking. The two main trails on this hike are the Ammonoosuc Ravine and Jewell trails, hence the trail name. Please note that you can skip the Camel Trail and Davis Path by staying far-left after the Lake of the Clouds hut to stay along Crawford Path if you wish - however, it's a similar mileage.
Expect a lot of scrambling up rocks, and a decent amount of time climbing through boulder fields. The hike down will be difficult on your joints no matter what route you choose.
When I went, it was a beautiful day on a holiday weekend, so there were quite a few people both on the trails and at the summit. I only experienced one "traffic jam" while hiking, but if you want to avoid crowds, I would hike this on a weekday if possible. Remember that people can drive or take a shuttle up to the summit, so there will likely be a lot of people at the top. It's not a quiet experience unless you find a spot to sit just below the summit. The good news is that if you wore yourself out too badly on the way up, you can take the train back down and it will drop you off near where you started.
I carried about 1.5L of water on me, but I think 2 would be ideal. You can refill at Lake of the Clouds hut, and at the summit, and I suggest doing so. You can also buy food and use the restrooms at both locations.
What to bring: Most of this hike will be spent above treeline, so remember to wear sunscreen, and reapply if needed. Also, anything below treeline is likely to have mosquitoes and other biting bugs, so bug spray is also highly recommended. Bring at least 2-liters of water with you if you can carry it and note that you can refill at the summit and Lake of the Clouds hut.
Facilities: There are restrooms at the summit of Mt Washington and at the Lake of the Clouds hut.
Camping: Dispersed camping is allowed beyond 200-feet of the trail along the Ammonoosuc Ravine Trail and the Jewell Trail, but no camping is allowed above the treeline. See this White Mountains PDF for more backcountry camping rules: https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5363715.pdf
Pets: Dogs are allowed if on leash and their waste must be carried out.
Waterfalls: There are two large waterfalls along this hike and both can be found along the Ammonoosuc Ravine Trail. The first can be found approximately 2-miles in while the second can be found approximately 2.5-miles into the hike up.