Zero Gully

A classic route with poor gear and belays. The climbing is not as hard as Point Five Gully, but the overall route is just as serious, and the paucity of any protection puts off a lot of climbers.

The base of the gully is between the Orion Face and Observatory Buttress.
P1) Easy angled snow-ice, with a steeper icy step leads to a belay at the base of a left-slanting chimney. In fat conditions you'll hardly notice the step, and a lot of climbers start higher, getting to the top of P2 in one rope length
P2) Follow the chimney to the top, belaying on a rounded spike. There is normally some tat well iced in, which gives a bit more comfort. A decent icefall can form above this stance too, possibly taking screws
P3) The crux pitch. Traverse right, across mixed ground and thin ice to get back into the main gully. Climb some steep ice steps to belay wherever you can find something to anchor to. A fixed nut in the left wall may still be there.
P4-7) Continue up the gully on good neve as it opens out onto the summit plateau. It's probably best to move together or just solo this last section: there isn't anything to belay off anyway!

The mixed traverse can be avoided by a variation on P2. Instead of going all the way to the top of the chimney climb steep ice on the right hand side of the gully. This doesn't affect the grade, but is probably marginally easier in fat conditions.

Start between the Orion Face and Observatory Ridge. The gully line is obvious, and the chimney of P2 should be obvious from the bottom

Not much. A rounded spike is often slung for the belay at the top of P2, and there could be fixed gear in the walls if you know where to dig. Other than this you'll have to improvise with tied-off screws and ice axe belays.