The Boulder Garden Loop is a nice loop hike on the west side of Mt. Si that starts at the Little Si trailhead. It features interesting boulders, moss, grassy lookouts, and a well-maintained trail. It is moderate in difficulty at 900 vertical feet of elevation gain and around 4 miles round trip. The following shows the route marked in yellow:
The trip starts as though hiking to Little Si, taking a right turn up the Old Mt. Si trail, climing 900 feet to where the Boulder Garden Loop splits off of the Old Mt. Si trail, then looping back to the Little Si trail.
A hike of the Boulder Garden loop can be combined with a climb of Little Si to double the elevation gain, or combined with a climb of Mt. Si to triple the elevation gain.
Directions to Trailhead: Take I-90 to exit 32, head north, then left on North Bend Way. In 0.3 miles you'll see the turnoff for Mount Si Road on the right. Follow the road 0.6 miles over the bridge, past the overflow parking lot to the Little Si trailhead parking lot on the left. A Discover Pass is required at the trailhead.