There are lots of good trips reports on Navajo and Niwot Ridge, but I'd like to add a few details and useful pictures for future climbers. Especially mere mortals like myself (experienced, but mid-40s and 20 lbs overweight).

I didn't realize how serious these peaks are. Comparable to Longs. Lots of Class 3 over an extended distance, and I think some Class 4 moves are probably required at the top of Navajo. There is lethal exposure in a couple of key places, and in the 30 to 40 mph sustained winds I experienced, it felt unsafe. I crawled the last wind-exposed bit to the summits just to say I made it, and then got the heck off of there. Also of note - no cell service on the most dangerous parts. You're on your own. Oh, and in case of bad weather or health problems on Niwot Ridge, the bailout options are not good - you can go illegally into the watershed to the south, or descend hideous loose gulleys on the north side for 1500 vertical feet.

The easiest way to get to Navajo is to hike to Isabelle Lake, keep going on the trail toward Isabelle Glacier, and then when you reach the glacial tarn at the foot of the headwall up to Isabelle Glacier proper, instead of turning right and ascending that wall, go due west (straight) past the tarn, following the feeder stream up, to reach a high flat area a little bit below 12,000 ft. Here's the view of the ridge line from there.

Look for Airplane Gully on the left. It's the far left gully in the photo above and stays Class 3. Here's a view from halfway up the gully.

You can top out through that tiny visible box of daylight left of center, or turn right at the sharp white rock, step over the airplane debris, and top out. Either way is fine - it's Class 3 everywhere, but the backside of the ridge is not exposed and totally navigable. You'll probably want to see the airplane, of course, and Navajo Peak is to the right anyway. The gully is a little loose and takes some care not to kick off rocks. If I weren't alone, I'd be mindful of my partner. You could descend this way, but it would be annoying.

Here's a view of the slope into the forbidden watershed once you reach the top of the gully.

Navajo from here looks very reasonable, and it is... right up until 20 feet from the summit. I couldn't find a Class 3 option and had to take a Class 4 line. From this point, the chimney right of center seems to be popular (not the same chimney used to climb Navajo from Apache). I didn't use it, trying to find something easier, but what I did ended up being Class 4 anyway. I'm normally very comfortable on Class 4, but in high wind with high exposure, this was not comfortable. Seriously consider your ability and the conditions. (Sorry no photos of this part - I was stressed out and focused on survival)

Assuming that works out, Niwot Ridge is serious Class 3. I liked it... for a while... until I didn't. It's beautiful and rugged and amazing, but nowhere to hide from the wind, and getting blown off the mountain here would make you a statistic. There are 3 major prominences on Niwot Ridge, and I believe the technical summit is the center one. That seemed pretty clear. So whether you approach from the gentle trail side of Niwot Ridge to the east, or you scramble over from Navajo, it's a little ways to get to the summit.

The plan was to do the whole Niwot Ridge and take the mellow tundra walk east back to the car. That seemed like a very relaxing way to get down. I think it's a good plan. Wish I had done it.

I did the west-most prominence for fun, and explored the ridge, but after the technical summit, I was exhausted. The third prominence looked too scary for my tired state and the wind was getting worse, so I made a poor decision. I thought I could just get down one of the north gulleys back to the glacial tarn and take the trail back to Isabelle Lake. Well, it is possible... I did it... but it's awful. Do not do this. I ended up with way more Class 4 moves than if I had just gone over the third prominence and taken the gentle ridge back to the east. Granted, those moves were out of the wind and less lethally exposed than the summits, but it was still an awful grind 1500 vertical feet down an extremely loose gully that kicked off rock slides with every step and required careful route finding around cliffs. Here's a picture looking back... but it's worse than it looks.

All that said, it is a BEAUTIFUL climb. One of the most scenic I have ever done. No ice (besides glaciers) as of Sept 19, though obviously that could change any minute now. Just take it seriously and know that it's a commitment once you reach the top of the gulley. I was aching all over by the time I trudged back to the car. Here's the unnecessary but beautiful best photo of the climb: