Namaste, I see a lot of tourist and visitors to Nepal ultimately ask for things to do in Nepal. So here I will try to list all activities that can be done in Nepal. You input will be highly appreciated as well. Please leave your thought in comment section.

Trekking

Annapurna Base Camp
Annapurna Circuit
Langtang
Manasalu
Everest Base Camp
Ghandruk / Poon Hill
Manang/Mustang
Kanchenjunga
Tilicho lake
Rara Lake

Peak climbing

Kwangde Peak
Lobuche peak
Pokalde peak
Island Peak
Mera peak
Tharpu Chuli Peak
Chulu west
Pisang peak
Singu Chuli Peak

Adventure Sports

Rafting (Trisuli, Bhotekoshi, Kali Gandaki, Seti, Karnali,Sun Koshi)
Bungee Jumping (Last Resort)
Mountain Flights
Kayaking
Canoeing
Chitwan Jungle safari
Bardia jungle safari
Camping
Fishing

Cultural Tours

Kathmandu, Bhaktapur, Patan Durbar Square
Kirtipur
Swayambhu/Boudha
Other temples in and around Kathmandu valley
Lumbini
Janakpur
Muktinath

Touristy Festivals

Holi, Indra Jatra, Seto and Rato Macchindranath Jatra, Bisket Jatra, Gai Jatra, Shivaratri

Places to visit in Pokhara

Lakeside
Mahendra Caves
Paragliding site
Zip Linesite
Mountaineering Museum
Sarangkot
Davis fall
Peace Pagoda

Other famous Places outside Kathmandu valley

Gorkha
Nuwakot
Bandipur
Palpa
Dolkha/Kalinchok
Other places like Rolpa/Dolpa in the Far-West
Kakani