The Gutter is a fine alternative to the Ghetto during the seasonal raptor closure which runs from February 1 through July 31 each year. While not as big or inspiring a bouldering slot, it's a handy place to get a pump, and can be combined with the Satellite Boulders, the Yarbles or the Compound to yield a nice circuit.
The Gutter sits directly below and east of the large overhang on the very left (south) side of the Second Flatiron. Approach via the Third Flatiron trail, but once at the Satellite Boulders (BBC in particular) cut right into the trees and follow the gully up to the base of the Second Flatiron. The Gutter will be on your right. It is a dark, left-diagonalling slot (what else?) with tons of chalk on the lip holds. Approach time: 20-25 minutes.
The traverse can be done many different ways, the easiest being to stay more or less on the lip, the hardest being to say more or less as low as possible through the beginning and middle. You'll encounter some very cool holds along this 90 feet of climbing: huecos, iron-rock flakes, tiny pockets and the ubiquituous Flatirons crimpers.
The Gutter is good in the afternoons during the hotter months but perfectly viable mid-day during the winter due to its slightly southerly exposure and rock slab landing, which is quick to melt out after a snowstorm.
Protection
Since this is a slot a crash pad won't do you much good. Wear a thick t-shirt so you don't raspberry your back if you crater.
This is one of my favorite traverses but I think it's really overrated difficulty-wise. The most natural way to do it for me starts on the lip, moves down below the lip to a flake, rest after the flake, go almost straight up to a jug high on the lip, rest, move down off the lip to a hole and left on some slopers, then almost straight up again to another rest on big holds up high, then the crux section moving down off the lip again on crimps so low that it's difficult to keep off the slab below, then more hard moves getting back up to the lip, and finally some easier moves along the lip to the finish. Seems like this way is about a V3????
I've gotta say this is probably the coolest traverse in Boulder. Technically, it isn't too tough. There are two sections where the moves are difficult to find, but I think the rating is probably around V6-V7. No one move is tougher than V3, but its very long and pumpy. The best thing to do is just to go find it and have fun.
This is a pretty fun traverse, reminiscent of some of the super long, little-known traverses (like Norwegian Wall) on West Mountain at Hueco. I have to disagree with the grade, however. A V6/V7 rating translates to someting like 5.13-. I think 5.12 endurance is about all that's required to send, so I'd be more apt to give it V4/5.