I’ll update this with miles, etc.
1. Lake Washington. From my house: down to Marymoor (early, before people get up — even then, you’ll be dodging walking clubs/jogging threesomes), N on Burke-Gilman around the top of the lake*, then follow the UW-Seward instructions to get to Lake Washington Blvd, take that to Seward, Seward to Jean Coulon, then take the trail up along the W side of Lake Washington that kicks you out at the I-90 Coal Creek underpass. Added bonus: throw in some Mercer Island loops for extended hill work to hit your distance/hill goals.
* I love the stretch through Woodinville/Bothell early in the morning, when no one’s there and it’s still a little bit cold as you whip through the turns. The poor trail condition (roots! roots! roots!) down to and through the UW is hard. Burke Gilman through Redmond becomes more and more dangerous as morons fill it, to the point where you may as well sit up and soft-pedal it through.
2. Duvall-Snohomish-Monroe-Duvall. I used to ride this all the time when I lived out there. Head out from Duvall and follow the Flying Wheels route. Pretty easy on the hills. Lots of easy rural roads. Only problem is you’re exposed with short shoulders on some curves, which would be scary if there was more traffic. For added fun, you can throw in the loop down to Carnation.
3. Not-so-Chilly Hilly. 33m, ~2600 feet of climbing. Take the ferry out to Bainbridge, do the Chilly Hilly route. Repeat as required to reach your distance goal, or until you die. Beautiful. Also painful as all hell, especially if your friend is (say) 25% lighter than you are and likes to kick your ass up long gradual climbs. Seems like it’s hard to get food/water during the ride.