THE MOMENT THERE is even a semblance of light, Ross crawls out of the tent and through a monocular studies the wall of Nyambo above us.

During the night, using a Russian 1:200,000 topo, altimeter readings, and GPS coordinates, I pinpointed our location. But these are just numbers. They establish our position, but not the conditions—the hollowness or hardness of the ice, the depth or danger of the snow, our fatigue or faith. These, the actual exigencies of a mountain, can be ascertained only the old-fashioned way.

"Which couloir looks good?" I ask.

"None," says Ross, handing me the monocular.

There is a 100-foot-deep cornice hanging over the breadth of the face. Our best option appears to be angling northward, crossing avalanche chutes, trying to climb largely on the rock ribs.

What enthralls me most about entering Unknown country is that you have to make it up as you go. There's no rule book.

The first few hundred feet are a scramble, then the face steepens and we are confronted with the appalling insecurity of the rock—thousands of feet of sharp, irregular blocks stacked one on top of the other and held together only by the mortar of ice. Pulling out any chunk might bring down a million tons of rock.

Plan E: Forget the cornice, climb yet another couloir.

Had Nyambo been previously ascended, we would have already known what to do, and for me, much of the mountain's magnetism would have been lost. What enthralls me most about entering unknown country is that you have to make it up as you go. There's no rule book. Improvisation is imperative.

And yet there's something even deeper, something even more seductive, about exploring one of the millions of slivers of terra incognita left all across the planet: If no one has been where you're going, you have no idea whether what you want to do can be done. The reason to go is to find out. The reason to go is to find out whether you can do it. Whether you have the nerve and craft, the resilience and resourcefulness to think on your feet and dance on your fears.

Unroped, swinging ice tools, Ross and I gradually ascend a web of interconnected couloirs. It's sometime in the afternoon when we stop at a ridiculously insecure belay. Spindrift is flying around our faces.

"We're moving too slow!" I shout over the roar of the wind. Ross nods. Yelling back and forth, we discuss our options. Continuing upward, whether we reach the summit or not, will guarantee an exposed, bagless bivouac. Hypothermia certain, frostbite probable. I stab my finger downward, and we turn around.

We rap off several disconcertingly small rock fragments frozen into the wall before finding a gully we can downclimb. It's a long haul back to the tent, where we both collapse.