What exactly you want to do in Nepal? I mean I have been to Nepal many a times for trekking and it is primarily a trekking destination. Let me know and I can suggest accordingly.
If you are a pro trekker, go for the Everest Base Camp. My friend in Punjab went there last year without any guide but yeah he has been to all the major hard treks here in India.
If you are an adventure seeker, I recommend to trek Annaburna Base camp, Annapura Circuit or an eat Ghandruk trek.
A visit to Jomsom, Mustang, Muktinath, Tilicho lake if you are looking for offbeat destinations. Also, Lumbini, which is a birth place if Gautam Buddha. Thank you !!