Wamena is the valley's only town of any size, and every trek begins in it. From here, guided itineraries stretch from a half-day walk to the bridge over the Baliem River to thirty-day expeditions deep into the territories of the Lani, Dani, Yali, and even - eventually - the Asmat. The town itself is functional: bank, post office, small hotels, three big markets, bicycle rickshaws called becaks that work as informal taxis. Prices are higher than anywhere else in Indonesia because everything arrives by air freight. A cold beer is not available at any price, because the Baliem Valley enforces a regional prohibition on alcohol. Kopi Wamena, the local coffee grown on the surrounding slopes, is what you buy instead.

The path you walk today may not exist next month. Landslides during the wet season routinely take out long sections of trail, and detours involve bushwhacking through secondary forest until you pick up the route again on the other side. Many treks climb from 1,800 meters at Wamena to over 3,000 meters at the passes between valleys, and the day's walk typically involves descending to a river crossing at the bottom of one valley before climbing over the ridge into the next. The trail from Wamena to Ungurruk takes three or four days on the standard routes. One variant goes down Mount Elit on makeshift wooden ladders for four consecutive hours - a stretch that turns genuinely dangerous in rain. Southern valley routes can run eight to ten days through villages, jungle, and high muddy plateaux where there is no map, sometimes no trail, and nobody to ask.

If you never leave town, spend a morning at the main market. The produce section alone is a study in Papuan agricultural diversity - sweet potatoes in half a dozen varieties, winged beans, taro, the local crayfish called udang selingkuh which translates, unhelpfully, as 'cheating shrimp.' Beyond the produce, the market sprawls into a full open-air shopping mall: clothing, canned goods, auto parts, farming tools, cheap electronics. Please ask before photographing. The bridge over the Baliem River just beside the market is where locals come to bathe, wash clothes, fish, and dig gravel, and where Dani and Yali families from remote villages arrive to sell vegetables and buy manufactured goods. On market days, you can watch an hour of this traffic and understand the valley's economy better than a government report would explain it.

Water from natural springs upstream of any human settlement is generally cool and generally safe - but this is your responsibility, not your guide's. Carry a backpacker's filter, or boil. Wamena city water is not safe without treatment. Hotels and restaurants supply boiled and filtered water; bottled water comes in half-liter to twenty-liter sizes from small local purification facilities. The altitude will affect you - mild headaches and shortness of breath are normal for the first twenty-four hours, and the cool nights can surprise anyone expecting tropical heat. Night walking in Wamena feels safe in practice, but stay alert and avoid flashing expensive items. Respect local customs. Ask before entering a honai, the circular thatched house that is the traditional Dani dwelling, and never photograph sacred objects without explicit permission.

Eighty-seven years ago, Richard Archbold's expedition flew over this valley by accident and saw a Neolithic civilization of two hundred thousand people farming sweet potatoes in a landscape nobody outside New Guinea knew existed. The valley was not erased by the subsequent decades of contact. Christianity arrived. Indonesian administration arrived. Tourism arrived, in small numbers, after the region opened up in the 1980s. But the Dani, Lani, and Yali still farm the same valleys, still build the same honai, still hold the Baliem Valley Festival each August. A trek here is not a trip to a theme park of the past - the valley is living, modernizing, and complicated. It is, however, one of the few places left on Earth where the distance from airstrip to stone-tool agriculture is measured in hours, not centuries.