I'm going to attempt to make this short at sweet. This hike is tough - in my opinion it's tougher than Mailbox Peak and it's not close. I started my day early, arriving at the trail head at the school bus turn around point on Mt. Si Rd. at about 7 AM and hitting the trail soon after.
The section to the falls is pretty easy. The first 1.5 miles (complete estimate, this trail is not on Green Trails Map 206S) is very easy, part of this section following a logging road and then part of it following easy gentle trail. There is a small cairn noting where to turn. After you reach the sign for Kamikaze Falls (also called Teneriffe falls) the trail becomes rocky and starts climbing for about a mile up to the falls. This section is still pretty easy and it's here that I started to get my first looks out across I-90 to the hills to the south. The falls themselves were quite pretty as they cascaded down the hill.
I've seen the section of trail from the falls to the summit quoted as about 1 1/2 miles. I think it could be closer to 2 but I don't know. What I do know is that its brutal (both going up and coming down). It's very rocky and very steep. You really need hiking poles and a very sturdy pair of boots. The trail essentially climbs east from the falls to the ridgeline and then follows the ridge all the way to the top. This was by far the most difficult section of trail I've covered this summer. The total climb from parking to summit is about 3800 feet and the vast majority of that elevation gain is above the falls.
I was very happy to reach the top just under 3 hours since leaving my car. Someone has built a cairn on top. The wind was blowing on the north edge of the summit but on the south edge I found a warm spot in the sun to relax and stare at Mt. Rainier. Mt. Si was immediately to the right of my resting spot and Mailbox Peak to my left. I could also see downtown Bellevue and Seattle from the summit.
Finally, below I put together a series of photos that will give you an idea of the 360 degree view.