Multiday backpacking trip linking up trails to do a lollipop/loop of sorts from White Pass. This was when the smoke and air quality was really bad, so I ended up changing plans and final route was:
Day 1: White Pass to Goat Lake 20.2mi / 5,627 gain
Day 2: Goat Lake to Horseshoe Lake 22.9mi / 2,326 gain
Day 3: Horseshoe Lake to Looking Glass Lake 15.89mi / 3,077 gain
Day 4: Looking Glass Lake to Midway TH PCT 20.64mi / 2,058 gain
Day 5: Midway TH  to Snowgrass Flats PCT 20mi / 3,297 gain
Day 6: Snowgrass Flats to White Pass 21.31 / 4,032 gain

TL;DR:
Most of these miles are forest miles with little to no view. The main highlights are the basin before knifes edge ridge, the ridge itself, goat lake and snowgrass flats area, and a few views on the PCT of Mt. Adams. The trail is in great condition and well traveled with PCT hikers. A few blowdowns and brushy areas, most notably lots of loose tread so puffs of dirt with each step. Berries were ripe!

Road Conditions: Great! Paved all the way to White Pass, and trailheads have pit toilets and privys. There is camping on the north trailhead for White Pass. I also walked several FSR on day 2: FSR 21, Walput Lake Rd, FSR 56, and FSR 2329 were all in great conditions and would be fine for any vehicle travel.

Trail Conditions: 
PCT: In great condition. very easy to follow and well established. A handful of blowdowns and maybe a few little brushy sections, but mostly in great shape. There are some steep climbs and the knifes edge which has some narrow scree sections and a couple snow crossings still, but the boot pack is good and otherwise solid trail. 

Goat Ridge: similar to PCT, well traveled and popular so in pretty good shape, nothing too notable here. I will say for Goat Lake, despite it being the worst smoke/haze air quality there were still easily 15-20 tents. I'm surprised there's no toilet here as it's higher alpine and very popular, so be prepared for that. 

Klickitat: I hesitated to add this to the list of trails as I only walked a couple miles from the Goat Ridge TH, but it was enough blowdowns and brush to slow my pace, and I was trying to make miles. Also the views were still hazy and felt the effort wasn't worth the brushy time. I'm not sure if the trail clears more along that side of the trail, but felt like I was one step away from losing trail as it's not well defined, but doable. 

Killen Creek: similar to PCT, well traveled and popular so in pretty good shape, nothing too notable here except it's a pretty steep and consistent climb up to the PCT. I started my morning with this climb and was feeling pretty knackered when I reached the junction. Signage is good for high camp and view when you reach the top is worth the effort. 

Round the Mountain / Looking Glass Lake: similar to PCT, but a little more rugged feeling. Only did round the mountain for a mile to the lake trail junction. This is in an old burn area, so the lake has a couple sites, but is definitely in the middle of a skeleton forest, so just heed caution with where you set up camp. Views of Adams are quite nice. There are a couple of creek crossings getting down to the lake, but fairly easy to cross. 

Animals/Bugs: Not a ton of bugs or enough to be problematic. I surprisingly didn't see any bears as the berries were starting to ripen I thought I may. I saw the usual chimpunks, birds, squirrels, and marmots! There are TONS of marmots near Goat Lake. I saw a squad of goats on the last day in the distance basking in sun. 

Water sources: Water was never an issue on this trip. I would say the driest section is from the knife's edge basin to White Pass, which is about 10 miles. There are couple trickles you could collect, or go to Shoe Lake before hitting white pass. I knew it was drier so filled up in full before making that last section of trail. Otherwise I didn't have any major issues.

Other: Berries were ripe and delicious! There are lots of really beautiful campsites along the PCT and views of Mt. Adams are spectacular. My thoughts were this should be named "Marmot Rocks Wilderness" as there were more marmots seen than goats, but then I thought maybe the metaphor is YOU are the mountain goat, travelling up and down the rocks. :-)

Happy Trails!

Didn't do the full trail; started at the western terminus at Forest Road 024, and went just over 5 miles before turning around, getting a little farther east than the trail head indicated on this site. FR 024 is full of potholes and ruts; at one point I had to get out of the car and walk to find the best place to cross the deep rut in my car (which has 9" ground clearance).

Snow fields at about 5200 feet and above, sometimes stretching for a quarter mile or so. Up to 6 feet deep in the shade still. That doesn't stop the mosquitoes, though. Strongly recommend bug spray. I counted over 80 bites after returning home.

Trail conditions are good; some work has clearly been done for the race that passes through here, as indicated by the trees that have been cut. See photo. A few areas of erosion, but nothing that felt too dangerous.

Beautiful, empty trail with great views. No cars at start, nobody else seen or heard in 10.5 miles.

Started at the north trailhead and headed south. Didn't see another soul on the trial for the two days we were out. Had planned to camp at Jackpot Lake or thereabouts however didn't realize what a massive climb there was between the trailhead and our destination. We might have made it except that at the top of the climb we found ourselves on a narrow ridge that looked like it would require mountaineering skills to cross. Instead of testing our luck, we made camp on a small patch of horizontal ground just before the ridge; otherwise there are not many great campsites along the trail. Additionally there was not any water between the trailhead and the ridge; luckily we had brought a large water bladder with us but water was always on our mind. In the morning there were large cat prints in the volcanic soil around our tent. My hiking companion and I are probably intermediate level backpackers -- we've been doing it for many years but definitely wouldn't claim to be experts. We look back on the trip with fondness but it was one of the most remote and isolated climbs we've done. An inexperienced hiker could run into serious trouble out there and everyone should be thoughtful about how much water they'll need to carry.

Jackpot Lake Trailhead to Saint John Lake via the Klickitat Trail. The trail is overgrown in places, bushwacking through berries and climbing over trees but doable for both a 10 and 12 years old. Shaded the entire way and nice tread. Trail can be a little hard to find due to lack of use but look up for orange or pink ribbon on trees to located your next steps. 6.25 miles and elevation gain/loss was minimal. Saint John Lake had a small camp site suitable for two or maybe three small tents. The water was warm and kids enjoyed swimming.  Great peek a boo views of Rainier, Adams, Saint Helens, and Hood. We scrambled and located the Sanctuary Arch (WOW!). We didn't see anyone else until we got back to our truck.

Started from an unmarked spur trail 12.5 miles up FS-20 from US-12.
(46.4686, -121.7046)
Road is in good shape as far as forest roads go.
The Klickitat Trail doesn't seem to get used much. Not even a single other person here on Independence Day. Trail getting overgrown in places but still easy to follow. Lots of meadows and wildflowers.
It's just over 5 miles from the car to Pompey Peak plus another mile round-trip to Cispus Lookout.
On the way to Pompey there are 2 side trails connecting to forest service roads. Keep right at both junctions.
11.5 miles and 2200' total.