The trek from Khumbu over the Salpa La to the Arun Valley starts on the main Everest tourist 'highway' in Solu Khumbu and diverts into more adventurous parts heading southeast through the eastern district of Sankhuwasabha, crossing three ranges and two major rivers to reach the Arun Valley. It is an interesting traverse through a variety of cultures and ecosystems. The route follows the same ground, albeit in reverse as H.W. Tilman on his approach to the Khumbu Valley in the autumn of 1950.
If you've already done the big three - Khumbu, Annapurna and Langtang, then this might be your next challenge. The trek from the Khumbu to the Arun Valley would make an ideal add-on following a successful trek in Khumbu, and a 'backdoor' alternative to the common Jiri 'walk-out'. Some sections of the trek can be very steep and are more taxing than anything on the main Solu-Khumbu trek despite the generally lower altitudes. There are some precarious bridge crossings but nothing really dangerous, given that there is in fact a long established porter route along much of the way. Even for the novice trekker the route should not be out of the question, given a little commonsense.
You can finish the Arun Valley trek at the Tumlingtar Airstrip, or further south at the road-head near Hille. There is enough of interest along the way not to rush this trek, however be aware that there may be a day or two waiting for the plane if flying out from Tumlingtar.
The route can be strenuous at times crossing three sizable passes up to 3350m. You might at times crane your neck to see the path ahead as it climbs into the clouds above. For the most part these climbs look worse than they are, but this trek is certainly a step up in difficulty from the Jiri to Lukla route. Trekking in places like this can be as much psychologically, as physically demanding, however, the trek is not difficult if taken at a sensible pace. At times it can be a very remote and wonderful landscape, however, disappointingly, other than at one or two viewpoints, there are not great mountain views.
Culturally, the Arun Trek is very interesting - moving from Sherpa through to Rai villages, then down to Chhetri and Brahmin villages. Despite the chain of basic lodges, impromptu lodgings can be found in keeping with traditional hospitality throughout Eastern Nepal. Only one village, probably Brahmin, insisted that I should continue on my way, and would provide me no food or lodging - otherwise you will usually find helpful and generous people when you need them.
The Arun Trek remains off the main tourist map being so don't expect a great social scene. With the lack of general development along the way the villages and their inhabitants retain a certain innocence to the Western eye. In early May 2001 I saw on average one other trekker per day. While most of the apple-pie crowd remains quite unaware of the existence of this easily accessible trek, the lodges are there and are eagerly awaiting guests.
The day-by-day itinerary described is a generally fairly conservative. Feel free to walk through to the next stop, but make sure that you allow plenty of time to reach your destination well before dark. In these times it would be unwise to continue trekking or wander too far after dark.
I accept these words of guidance are a little sketchy and lacking detail at times. Please feel free to offer updates and corrections using the comment system on the trekking pages