The Manaslu Trek (or Manaslu Circuit Trek) is a 14-day tea-house trek which circumnavigates the 8th highest peak in the world (8,156 m). The trek has all the elements of other treks in Nepal including both Hindu and Buddhist culture, protected wildlife, rhododendrons and wild flowers, raging rivers, precarious bridges and stunning mountain scenery.
The trek is much easier than it used to be with greatly improved trails along the Budi Gandaki river gorge. In terms of difficulty, it is comparable with the Annapurna Circuit Trek or Everest Base Camp trek. Its highlight is undoubtedly the spectacular unhindered views of Manaslu.
Just over 2,000 people complete the trek per year with more than half visiting in October. This is substantially fewer than visiting Annapurna, Everest or Langtang. There are two main reason for the fewer numbers.
The first reason is that the trek used to require camping, as there were too few tea-houses along the trail. In particular there was no lodge below the Larkya La (a pass at 5135m) requiring an enforced night of camping. This is no longer the case. Since 2010 there is a tea-house below the pass and all the way up from the starting point. A few of the tea-houses are still basic compared to counterparts on the Annapurna Circuit, but most are comfortable.
The second reason is that the trek has restricted area status. This means it requires a special permit (see below), that the group have two or more members and that a registered trekking guide accompanies the group. In 2011, for Nepal Tourism Year, the permit fee was reduced to US$50 per week.
These two factors together have made the trek affordable for budget travellers and it is now being referred to as The New Annapurna Circuit.
Manaslu region is still under development for tourism business. In the past, visiting the remote parts of Nepal was only possible by camping trekking for adventure holidays. Due to the increasing number of travelers, small lodges in the major places are being developed. So, now you can trek by staying on local lodges (tea houses) without camping in this famous trekking area. Manaslu trekking can be done either way - staying at lodges (tea-houses) or camping.
You have to arrange this trek though a registered trekking agency, even though you may just be two people with a single guide. The agency is necessary for arranging the permit, as individual tourists are not permitted to do that.
The trek generally starts at Arughat. This is a simple 5-6 hour micro-bus ride from Kathmandu Dhading Bus Station or new bus park costing around US$7. Local buses leave early in the morning and no advanced booking is required. The local agency will provide you the bus ticket. It is also possible to share a private jeep from Kathmandu to Arughat which can be arranged by a local transport company.
Check the online Manaslu Trek map  to understand the locations mentioned in the itinerary.
Travel from Kathmandu to Arughat [600m good lodges]. The bus, or a local jeep, may take you further than Arughat depending on the state of the road ahead. Sleep there or continue to Arket [750m basic lodges] or Soti Khola [800m basic lodges] to get a head start. Otherwise the standard itinerary with days of 6 hours or less of walking is as follows:
It is also possible to start from Gorkha Bazaar which is quicker to reach from Kathmandu on a smoother road. You can find onward transport to Barpak, where there is accommodation, and continue via Larpak to join the main trek. A side trip to Tsum Valley is also possible. This used to require camping or pre-arranged homestays, but can now be done as a teahouse trek, staying at lodges (though facilities are more basic than on the main trekking route). Itineraries can be as short as 10 days, excluding rest days, or as much as 21 days, taken at a relaxing pace with plenty of exploring.
It is also entirely possible to combine with the Annapurna Ciruit: from Dharapani, continue to Manang and over the Thorung La at speed having already acclimatized. Then fly or bus out from Jomson to Pokhara. Others options include the trek to Nar and Phu, taking advantage of trek-earned acclimatisation and fitness.
Popular day trips include a visit to Manaslu basecamp from Samagaon and a hike to the border with Tibet which is a 5 hour return trip from Samdo.
The principal danger is altitude, specifically going too high too quickly. Taking a day for acclimatisation at Samagaon, Samdo, or Larkya Phedi may be helpful. Follow these instructions for altitude sickness prevention.
Another serious danger is being pushed off the trail by donkeys, which has resulted in the deaths of some trekkers. Be alert for the bells of approaching donkeys and make sure you are on the inside of the trail, out of the way of donkeys, and wait until they have passed before proceeding. There are also cases of trekkers being blown off of trails by wind.
Cold and wind can be dangerous, so suitable clothing is essential. Snow and ice may be a problem at the Larkya Lal Pass, and some trail sections and stream crossings may be icy, especially in November or later. Trekking poles and light crampons (aka minispikes) can be very helpful in reducing the risk of slipping, particularly on the steep descent after crossing the pass. Gaiters may be helpful in deep snow or blowing snow.
Himalayan Rescue Association  is an organization arranging / planning for emergency evacuations in the mountains.
Finally take a bus from Besisahar to return to Kathmandu, or continue onward to Pokhara. Another option, if you still have time and are interested in the Annapurna Circuit Trek (Thorong-la Pass, 5416 m), rather than coming back to Besesahar, you can start your trek to Annapurna from Dharapani right away. But do not forget to bring your TIMS Card permit because your restricted permit will not valid any more. However, your ACAP permit will still be valid. You will already have the ACAP due to the fact that you end the Manaslu Circuit in the Annapurna region. So why not if you have time for another adventure. Maximum in 1 week more and you will reach Pokhara. If you are an independent traveler, you could simply carry on without your guide or porter from Dharapani and head towards Thorong-la on your own. The Annapurna region does not require a guide to be with you as long as you have necessary the documents with you.