Depending on your interests, there are so many 'extra' activities in addition to trekking and sightseeing available in Nepal to fill many many memorable holidays. I provide a list below of some the common (and not so common) possibilities and am happy to make enquires on your behalf regarding costs/arrangements with reputable operators:

Biking Day Trips

Bird Watching

Boating

Bungy Jumping

Canyoning

Dolphin Watching

Fishing

Hot Air Ballooning

Mountain Biking

Mountain Flight

Mountain Viewing

Paragliding

Pony Trekking

Rafting and Kayaking

Rock (and Ice) Climbing

Scenic Drives

Sunrise and Sunsets

Village Tourism