Although you can do the Seven Lakes Trail as a round-trip hike from either end, it's frequently done as a short thru-hike from one trailhead to the other. There is no public transport, so you'll need to set up your own car shuttle. I recommend starting from the Engineer Trailhead, simply because that's the more difficult of the two trailheads to drive to — so you'll want to be sure both vehicles can manage it.
From the trailhead, the first mile or so of this trail runs near the shore of Engineer Lake, giving you beautiful views over the water. You'll also see a fork in the trail, where an access trail for the Engineer Lake public use cabin branches off to the right. Keep to the left to stay on the Seven Lakes Trail, although the name is a bit of misnomer. All told, there are just four lakes on this chunk of trail, two of them accessed by short spur trails.