A local favorite loved for its closeness to town, ease of access, and counter-clockwise loop that separates uphill and downhill traffic.
Park at the New World Gulch trailhead and proceed up the obvious trail along the creek. When you come to the first fork of two watersheds follow the trail skiier's right up the creek bed. Unless you arrive very early in the morning, there will almost certainly be a skin track already in.
Make your way until you come to a large-ish meadow and again follow the skin track to the right up and into the woods. Gain the saddle between Mount Ellis and "Little Ellis", enjoy the view down into Bozeman and then follow the ridge skier's left toward the summit of Ellis, picking your stopping point based on where you wish to descend.