Little Si is the smaller companion of the much more challenging and ominous Mount Si. Little Si is more our style - takes about 3-4 hours, a solid 4.7 miles, and doesn't require you to pack a meal to keep from turning into a monster halfway through. It's also relatively close to Seattle, so you don't spend too much time in the car getting there.
Little Si is great year round - it is fairly protected from the elements so when we did it in January we stayed pretty dry even though it was raining most of the hike. The trail is well kept and offers great checkpoints along the way to keep you entertained, including rock climbers doing some scary climbs on the cliffs or pretty creeks running through the trail.
The hike is rated moderate on WTA.org, but we think it is fine for beginners. There are a few switchbacks, but those are few and far between on this hike, with the majority of the trail being moderate inclines that will keep your blood flowing, but you won't be keeling over from exertion. The very end is tiring, but the reward of the views at the top will keep you going!
Once you get to the top there are two viewpoints, one to the left of the trail right as you come out and then another a bit farther up that allows you to see a more 360 view of the area. Check out both, but the first viewpoint is the truly stunning one, with Mount Si looming above you.
Check out the trip reports before you go at WTA.