Annapurna south is the 10th highest mountain in the world and was the first 8000m peak to be climbed. It was first summited in 1950 by Maurice Herzog and Louis Lachenal. It was not until 1970 that Annapurna was summited again. In the autumn of 1999 there were 120 expedition to Annapurna . 106 climbers reached the summit. 54 climbers never came back. However, I am assuming you are more interested in trekking the Annapurna region , so most of this information will pertain to trekkers considering this trip. The best season to climbing is usual trekking season in Nepal is from October to May. The rest of the year is the monson season and is not desirable for either trekking or expeditions. Besides the cold and rain, leeches are a problem during the monsoons. If you are going to be trekking to Annapurna , October and November are the best months.
Trekking possibilities are quite varied, but most will start at Pokhara. The circuit trek to the Annapurna Sanctuary will take at least 10 days, but allow 14 to have time to enjoy it and to allow for unforseen events. The route up the narrow Modi Khola river valley is quite wet and slippery and quite steep in a few places. It can be a bit dangerous. The trail up to the Annapurna basecamp is a more serious undertaking.
Day 1: Arrival Kathmandu, transfer to Hotel & well come Diner.
Day 2: In Kathmandu
Day 3: Prepared Expedition & Briefing in Ministry of Tourism
Day 4: Drive to trailhead Beni (830m) and overnight at hotel
Day 5: Trek to Tatopani (1190m) and overnight at hotel
Day 6: Trek to Ghasa (2010m) and overnight at hotel.
Day 7: Trek to Lete (2480m) and overnight at hotel
Day 8: Trek to Thulo Bugin and overnight in jungle camp.
Day 9: Trek to Thulo Bugin pass and overnight in river camp.
Day 10: Trek to Mristi Khola and overnight in river camp.
Day 11: Trek to Base Camp.
Day 12-47: Climbing period.
Day 48: Cleaning up base camp.
Day 49: Trek back to Thulo Bugin and overnight at hotel.
Day 50: Trek back to Lete and overnight at hotel.
Day 51: Trek to Tukuche (2590m) / Marpha (2627m) and overnight at hotel.
Day 52: Trek to Jomsom (2710m) and overnight at hotel.
Day 53: Fly back from Jomsom to Pokhara and transfer to hotel
Day 54: Fly back to Kathmandu and transfer to hotel.
Day 55: Kathmandu leisure/ rest /sopping
Day 56: International Departure.