Sagarmatha National Park

A 14-day winter route to the Gokyo Lakes and Everest Base Camp, done on Dec 23, 2021 - Jan 05, 2022.

Logistics. The entrance point is Tenzing-Hillary Airport in Lukla, which is connected to Kathmandu by regular morning flights. The round-trip costs about $300-350.

Costs and Fees. In Lukla you will be charged 1800 rupees as a municipal entrance fee into the community. The entrance into the Sagarmatha National Park will cost additional 3000 rupees for non-residents. Dwelling and food is provided by lodges, in large villages most of them are open even in winter. They usually ask 200-500 rupees per 2-bed room, but sometimes they also offer free dwelling if you order food. The food expenses for 1 day will sum up to about 3300 rupees. You need to have cash, US$ are widely accepted.

Acclimatisation. Be sure to follow the standard acclimatisation technique during the first 6-8 days of the ascent: do not hurry on the uphills and do not stay overnight on your daily max altitude. In our case, we did the following:
DAY 1: Lukla to Monjo + a loop to Everest Viewpoint below Namche Bazaar;
DAY 2: Monjo to Namche Bazaar + a loop to Khumjung;
DAY 3: Namche Bazaar to Phortze Tenga with an ascent to 4000 m along the way;
DAY 4: Phortze Tenga to Nachermo;
DAY 5: Loop from Namchermo to Gokyo Ri without backpacks;
DAY 6: Machermo to Gokyo + a short loop to lake Donag Tsho.
At this point the acclimatisation was complete.

Weather. Winters normally have more sunny days in this region, than other seasons, although occasional snow showers are possible. In our own experience, we were stuck in Gokyo due to a massive snowfall which lasted for 30 hours and built up a ~40 cm mantle. Thus we abandoned our initial plan to go on the Cho La Pass, and for the next 2 days we had to break the path in the snow on our way down to the EBC track.
Temperature wise, you should be prepared for cold nights: ourselves had frosts down to -22C, and the shelters provide very weak protection (bottles with water are frozen in the morning). Daytime hours are much milder (-5..+5C) and are comfortable for walking.

Gear. No tents or caremats are needed, as lodges provide beds with blankets. A warm sleeping bag (extreme Temp -10C or lower) is a must. Although crampons might be useful if you are intending to cross the glaciers (we didn't), it is more preferrable to have microspikes: the tracks can get really slippery on the slopes.

As a conclusion, this track will be quite easy for the experienced hikers, but will imply endurance of the cold and altitudes. Gokyo Ri and Kala Pattar offer the most exciting viewpoints. Dingboche and its surroundings also have marvellous scenic spots on the mountains. EBC itself is desolate in winter and is not very interesting.