The Annapurna Circuit is a popular name for a trek within the Annapurna mountain range of central Nepal. I did the 240km trek in 2011 with a side hike to the Tilicho Lake (4950m).
The trek rises to an altitude of 5,400m on the Thorung La pass, touching the edge of the Tibetan plateau. This trek crosses two different river valleys and encircles the Annapurna massif, crossing Thorung La (5416m), the highest pass on this trek.
Our trek took about 18 days, leaving from Kathmandu with the bus-hellride to Bhulbhule ( https://www.youtube.com/watch?v=2oR61FZ1wiw / German text ). The trail is moderate to fairly challenging and makes numerous river crossings over steel and wooden suspension bridges.
Tea houses and lodges along the circuit are available for meals and accommodations. Some groups may opt for tents but these are typically only for those destined for side trips away from lodges such as climbing a peak.