The approach hike to langtang starts out with downs and ups, then slowly uphill. That calls for alarmbells to ring; it is easy to come down to altitude sickness here. The altitude gain deceptive and you really do need to watch out and not push ahead, too much, but remain with short day hikes. The walking times stipulated here I obtained from a Dunche hotel host with good experience.
In the old days we started at Dunche, via Bharku (2 hrs) and Syabru (another 3 hrs) and down to Syabru Bensi at the river crossing (2,5 hrs).
These days you start at Syabru Bensi and go to Khangjung (3 hrs), on to Sherpagaoun (3 hrs), and Sherpagaoun to Rimche (1 hr).
From Rimche to Lama Hotel (20 mins), on to Gumnachowk (1,5 hrs), Ghorapa Tabela (1,5 hrs) and by now you have reached 3000 meters. A lot slower than up to Sing Gompa, but the rest is apparently the problem point here: you slowly gain altitude, and so there is no rescue, no way do escape to lower altitude if you catch AMS.
Ghorapa Tabela via Thangshjap gumpa to Langtang village is 3 hrs. From Langtang village to Kyangin Gompa via Mundu and Sindum is also 3 hrs. From Kynagin Gompa with its good lodges and facilities you can take day excursions into Upper langtang Valley.
The hike to Gosainkund lake and beyond is surprisingly short and fast. That calls for alarmbells to ring; it is easy to come down to altitude sickness here. So the hiking distances are deceptively short for what you actually need to get to Gosainkund. Not staying overnight at Sing Gompa/Chandanbari and/or the Laurebina lodges can be risky. The walking times stipulated here I obtained from a Dunche hotel host with good experience.
Dunche-Sing Gompa 5 hrs (I did it in 3).
Sing Gompa-Cholang pati - Laurebina lodges 3 hrs (I spent much longer, taking in the surroundings).
Laurebina-Gosainkund 2 hrs (could be more depending on altitude tolerance and snow cover).
Gosainkund-Laurebina La pass 1 hrs.
There are 3 buses a day from Kathmandu to Dhunche and 2 of these carry on all the way to Syabrubensi via Thulo Bharkhu. The bus ride as far as Trisuli Bazar is relatively smooth ride, though there are quite a few military/police checkposts where the majority of the Nepali people on board the bus have to get off and walk through, this adds at least a couple of hours onto the journey. After Trisuli the road deteriorates badly and the bus takes 5 hours to travel approx 40km! This section of road is also prone to landslides, especially in the monsoon season. Buses are still prone to breaking down on this section due to the many huge boulders and the condition of the ageing buses. The first time I travelled this route my bus also broke down and we had to walk a good 30 mins before a jeep would give us a lift. Having said all of this, the route is spectacular if a little scary and even though it is a long journey I think it is a much more fun way to travel than to take a private jeep, which is the other option to travelling this route.
A sort of local bus proceeds from Syabrubesi toward the lead mine road south of Pabil.
The bus apparently goes about 20 km past Syabrubesi, up the switchcbacks (see photo). Past the 20 km mark hardly there is hardly anybody permanently settled.
Coming up from Kathmandu and Trishuli Bazaar, the bus will stop at Dunche first (most convenient for direct ascent to Singh Gomba and beyond next morning), at the trail head for Barkhu village (for Barkhu and Thulo Syabru and the south bank of Langtang and up to Singh Gomba and Laurebina Yak/Gosainkund), and finally the end stop is Syabrubesi, all the way down to the river. This stop is the most convenient if you want to proceed into the Langtang Valley proper.
From Kathmandu (0 km) the road climbs out of the valley past the Nagarjun Royal Forest and enters a steep terraced hill landscape. Here you leave the KTM Valley rim. Right after the top of the pass below Kakani there is a village called Ranipauwa, where there is a major market for moola, the white radish. Also a good place for a cup of tea and breakfast. Good view from here toward Ganesh and Langtang Himal. Then you zig-zag down the slope into the Trishuli Valley, and reach Trishuli Bazaar (70 km). Trishuli is only at about 550 meters altitude. Lunch break? From here you follow a relatively flat valley bottom along the Trishuli river to Bettrawati (80 km). Here's normally a checkpoint, and after that, very steep switchbacks way up the hillsideup to the villlage of Kalistan (more tea and snacks?). From above Kalistan the road levels out at about 1800 meters and follows the contours of the Gosainkunda Lekh broad western spur. Down below is the Trishuli khola, and the views to the north and west are great. There are some active landslips you have to cross. A checkpoint and some paperwork and a fee tells you you are entering Langtang National Park. A couple of kilometers further on is Dunche (118 km). You can get off the bus here (many lodges) and head up for Singh Gomba and Gosainkunda the next day, or continue further switchbacks down to Barkhu for a short walk to Syabru, or all the way down to Syabrubensi. The road continues to a lead mine in Ganesh Himal.
There are a couple of buses running all the way from Kathmandu to Syabrubesi each day. When I used these they were in a terrible condition - both the road and the buses. Now with the maoists around in the Nuwakot area I believe things are not much better. The maoists have probably added another layer of siphoning off the money from maintenance as "revolutionary fee" or better, mafia-style protection money.
Both times I travelled by bu, we had to get out of the buses at the huge landslide in the upper Trishuli Valley, 2/3rds of the way in from Betrawati to Dunche. The bus, empty, save for the driver, sped across the rubble as fast as possible. Below there is a 1500-meter scree drop. I once hired a car also, but that trip was so bumpy that I returned by the long-bed bus. That was the supersonic one (said so!) with the vomit streaks on the sides....
Another time on this stretch I sat in the back seat and the back window pane started cracking - eventually falling down on us. By that time we had a clue of what was to happen so we donned mountain parkas with hoods over us and came out of it without a cut. With this special air conditioning we kept the parkas on the last 6 hours of travel...
Just be prepared for a long and difficult journey, and ensure you keep up your mood by bringing a thermos with something to drink, a scarf or some clothes to keep the cold and draft out, etc. It is a very photogenic journey, so with time and money at hand the best option is probably to hire a jeep and start very early in the morning and make many stops on the way.