Next to the busy Little Si Trail hikers can find the Boulder Garden Loop, which sees a fraction of the traffic. The name comes from the huge boulders that lay around the trail. Some of the boulders are two stories tall and completely covered in moss. The trail is well maintained, but it does get narrow at times.
The trail starts on the same path as Little Si, but it cuts off at around a quarter of a mile. There is a sign directing the way to the boulder gardens. Once the trails split, the Boulder Gardens trail becomes much steeper. The boulders are visible after a quarter of a mile, and most are covered in moss and other old-growth. Eventually there will be a sign directing you to the Boulder Garden Trail; ambitious hikers can also take a route to the Old Mount Si Trail.
If you continue on you will meet with the Little Si Trail at around a half mile into that trail. There are well marked signs along the way to direct you toward the right route.