Pokhara, a city in the eastern Nepal, is a starting point for trips and expeditions to eastern Himalayas. The well known Annapurna trek circuit could take around 16 days, but there are plenty of options for shorter treks, like a 3-4 day trek to Poon Hill.  You will report your trek plan and pay a fee to enter the Himalaya trekking zone. Your guides usually arrange these formalities. The accommodation is in small mountain villages. The scenery is stunning and you will pass also the river below.