Steep ups'n'downs make it too difficult for most riders, but for locals, it's a great workout. Connects to the Sammamish River Trail and Puget Power Trail. Can get swampy in the winter and overgrown with nettles in the summer. Basically the best part of the riding covers a series of ridges between the light industrial complexes on Willows Road in Redmond, up to the powerline above. The best trails are designed, created and maintained by mountain bikers, creatively using powerline right of ways and various easements. This trail system is deserted on weekends and only has a few mtn bikes and joggers/walkers at lunch time during weekdays. Only one small bit of connector trail is posted "no bikes". You can bypass that short trail so it is nothing to worry about. Neigbors seem ok with mtn bikes too.
The only trail to generally avoid is the original "Primex trail" which goes through the bogs at the bottom of the Fjords and is not designed to be particularly rideable anyway. Trails have been given colorful names. All are twisty and slow and challenging. They need a day or two without rain to unslime enough to be really rideable.
Current favorite out and back is to get into the system from the trail head for the We Who Trail which starts at the South end of the pond at the top of the access driveway that cuts between Data I/O and Metawave.
We Who is the only trail really designed for uphill climbing. When you reach the top of that trail you can take the first right for the most technical twisty dowhhill SKaM trail. Or you can push on and take the next right, drop to a 4 way intersection, take a left onto a cutoff over to the powerline. Take a right on the powerline, which will take you to the twisty Sniper Blind trail.
Left out of Sniper Blind will joggle onto Mad Dog or go right on the powerline and follow that up to the construction swath. A new tech area may eventually be put in on the other side of the swath. If you go down the swath, I recommend turning around at that point and backtracking, versus taking the Primex trail.
When you back track, and go back through Sniper Blind and the cutoff, go straight ahead at the 4 way intersection, then drop down twisty Heartbreaker (actually THREE descents are your option at that point, on all of the next three ridges). A new out and back is in work at the top of Heartbreaker, going down the ridge just north.
Main trick is to explore and keep circling back up We Who at the pond, when you come out onto parking lots at other points.
The descents are twisty and fun, but designed to keep speed down (please limit or avoid skidding).
How to get there:
From 405, take the 85th St exit and head east towards Redmond. 85th St becomes 908 and eventually Redmond Way. Make a left on Willows Rd. After about 1 mile, turn into one of the many office parks on your left. Wind your way west through one of the many parking lots and you'll eventually hit the woods.
There are several places to park, but the legal ones are not easy to find. You can park in one of the office complex lots (I haven't heard of anyone getting a ticket). Or park on one of the many side streets east of 132nd Ave (for example, take 97th St to 93rd Ct and there's a little trail at the end of the cul-de-sac that takes you to the southern most entrance to the woods). There is a discreet trail access at the top of that driveway, between the rock and wood retaining walls, which is a short bike push to the starting point on the south end of the pond.
There are other access points you may stumble upon as you explore.