Part of the glory of trekking in the Himalaya is how high you can go – because of the latitude, the snowline starts higher than the summits of many mountains further away from the Equator. However, this is not an environment to be take lightly, as the events in Annapurna National Park on 12 October 2014 tragically demonstrated. Dozens of trekkers perished after blizzards struck the upper stages of the Annapurna circuit in Nepal's worst ever trekking disaster. On any trek, it is essential to make sure you are properly equipped for the conditions, that you tell people where you are going and when you will be back, and that you monitor the weather and seek shelter promptly if conditions deteriorate.
So, what is it like to cross a Himalayan pass? Well, put ideas of knife-edge ridges out of your mind. Most passes in the Himalaya involve a slow, sustained ascent on one side, and a slow, sustained descent on the other. The climb will test your lungs and muscles to breaking point; the descent will do the same to your knees. False ridges abound, so you'll think you've reached the top, only to have your hopes dashed as another soaring ridge looms ahead. But you can't miss the actual passes – just look for the strings of fluttering prayer flags, left by generations of past trekkers and their Sherpa guides.
Those who successfully conquer the high passes of the Himalaya can join the exclusive club of high-altitude trekkers, and participate in the conversations that buzz around the bars of Thamel in Kathmandu. How did you feel at the top? Did you get any symptoms of AMS (Acute Mountain Sickness)? Did you take Diamox? More valuably, you'll gain the satisfaction of pitting yourself against a mighty natural obstacle and overcoming all the physical and psychological hurdles put in your way. For that reason if no other, the high passes of Nepal deserve a special place in the trekking hall of fame.
Nepal's most dramatic passes
For locals, crossing the passes – or la – that link the valleys of the high Himalaya is a daily necessity, particularly in Solukhumbu, where human habitation extends all the way to the Khumbu icefall on the flanks of Mount Everest. The meltwater streams that drain from the world's highest mountains have carved a tortured landscape of interlinked valleys that zigzag south towards the Terai plains like fossilised lightning. To get from Valley A to Valley B, the only option – short of walking downhill for days to reach the nearest river confluence – is to go over the top. If you feel like taking on the challenge, try our pick of the most testing passes in Nepal.
1) The Cho La (5420m)
While legions of trekkers charge north from Dughla to Everest Base Camp, a smaller contingent of dedicated trekkers veers west towards Gokyo, crossing the mighty Cho La, squeezed between the snowcapped summits of Lobuche (6135m) and Cholatse (6443m). This dramatic side trek breaks down into a scramble over loose boulders before emerging at the perfect, unblemished glacier which caps the pass. Bring sunglasses, and a wide-angle lens for the magnificent views back down the valley towards the perfectly-framed peak of Ama Dablam (6856m).
2) The Renjo La (5345m)
From the relative comfort of Gokyo, where you can fight off the cold with a hot flask of Nepali tea, the zigzag trail that climbs abruptly to the Renjo La from the western shore of the Dudh Pokhari inspires a curious sense of foreboding. But steel your nerves and you'll be rewarded with views of Everest that humble those from the crowded viewpoint at Kala Pattar on the Everest Base Camp trek. As preparation for the sheer descent to the Thame valley on the far side, focus your mind on the final gentle amble back to Namche Bazaar, and the ice-cold beer waiting for you at the world's highest Irish Pub.
3) The Kongma La (5535m)
Crossing the Kongma La, the highest of the Three Passes that link the high valleys of Solukhumbu, is not so much a trek as a precarious struggle for purchase on loose, skittering stones. But what views! As it climbs from the banks of the Imja Khola, the crudely marked trail offers views over a sawtooth ridge of ice-covered peaks, including two of the world's 8000-metre monsters, Lhotse (8516m) and Makalu (8481m). Pause for a moment of contemplation at the still and silent lakes just below the pass, then throw yourself into an almost vertical tumble over loose scree down to the Khumbu glacier.
4) Makalu Base Camp and the Sherpani Col (6145m)
The gruelling crossing from the Arun Valley to the Khumbu Valley will take you far from the maddening crowds. Only a handful of trekkers brave the trail from Makalu Base Camp to the Sherpani Col, perched at a head-spinning 6145m. The trek is just one leg of the epic 1700km Great Himalayan Trail, running the entire length of Nepal. This is not a trek for the faint-hearted – stages of the route involve technical climbing with ice axes and crampons, and hair-raising descents on fixed ropes – but few sights can match the crossing from Sherpani Col to West Col over virgin snowfields atop the Barun Glacier.
5) The Thorung La (5416m)
Nepal's most famous pass is crossed by hundreds of trekkers daily at the height of the season, but it was the scene of tragedy in October 2014 when blizzards hit the upper stages of the Annapurna Circuit trek, killing dozens of trekkers, porters and guides. Even in clear weather, the Thorung La is far from a soft option. The trail to the pass climbs almost 2000m from Manang, an ascent that must be staggered over three or more days to reduce the risk of AMS. The reward for all this effort is mesmerising views over the Great Barrier Ridge and the Annapurna range, with a prayer flag-draped chorten (Tibetan stupa) to pose in front of and a tiny teashop serving one of the most expensive, but welcome, cups of the tea in the Himalaya.
Staying safe at altitude
Altitude is not something to take lightly in the Himalaya. AMS is a risk on any trek above 2800m, and the chances of developing potentially life-threatening symptoms increase the faster you ascend. Always take the recommended acclimatisation days and follow the golden rules of high-altitude trekking – limit your rate of altitude gain to 300m per day, try to sleep at a lower altitude than the highest point you reach on any given day, and if you start to feel symptoms of AMS, descend immediately. The weather is also a critical factor; conditions can change suddenly and it's essential to seek shelter if the weather deteriorates. Sitting out heavy rain or snow in a teahouse is always a safer option than trying to push on to reach the next stop on your itinerary.
How low can you go?
There is no obligation to climb the highest passes. Some of the most rewarding treks in Nepal follow the winding valleys of the Middle Hills, passing through a fascinating tapestry of tribal communities. Even better, most 'cultural trekking' routes are well off the mainstream trekking circuit, so you'll see less Gore-Tex and apple pie but more of the real Nepal. Browse a copy of Lonely Planet's Trekking in the Nepal Himalaya for recommended routes.
Joe Bindloss is Lonely Planet's South Asia Destination Editor. You can follow him on Twitter @joe_planet.