You can easily fill a few months with biking, rafting, kayaking, canyoning and other adventures in the mountians and rivers surrounding the Kathmandu valley.
Some ideas ...

Spas & Health
BIKE TRIPS
Pokhara to Kathmandu
Mountain Biking - Nepal
An
epic mountain bike journey through some of the most dramatic mountain
scenery and traditional villages in all of the Himalaya, with jeep
support en route.
5-18
February (14 days) - off-road mountain biking with jeep support
- Kim & Lhakpa - $2480
Chitwan Wildlife Extension - $300
The
Great Lhasa Kathmandu Bike Journey - Tibet & Nepal
Join us for this epic journey from Lhasa to Kathmandu, an exciting and challening bicycle trip starting in once forbidden Lhasa. En route to Nepal we pass through traditonal villages, cross high Himalayan passes and end up in exotic Kathmandu. You can do this bike trip privately as well ...
June (24 days) - mountain biking & 3-star accommodation -
Kim & Bhutanese Guide - $4980
Private Departures Optional

RIDES IN THE KATHMANDU VALLEY
Kakani & Budhanilkantha
Biking to Kakani and then through the Shivapuri National Park to Budhanilkantha is an challenging day-trip from central Kathmandu. The trail from Kakani down to Budhanilkantha is for single-track mountain bikers and will be challenging for weekend or road bikers. Kakani, about 25 km from central Kathmandu past the Nagarjun Forest Reserve, is a view point at 2200 meters where strawberries are grown in the colder months. There is a restaurant and 'resort' at the top, so you can make a full day of cycling through this area. From the viewpoint, continue east along the dirt road past the local shops and into the national park, where you'll have to pay a NRP 100 entrance fee. You'll drop right into Budhanilkantha and then only need to cycle straight along the paved road which passes through Bansbari, Maharaganj and Lazimpat to reach central Kathmandu.
Nagarkot, Thimi, Bhaktapur & Changu Narayan
Biking through Thimi to Nagarkot and back via Changu Narayan is a 75+ km daytrip from Kathmandu. It's 38 km from central Kathmandu to Nagarkot, the last 17 of them steeply up a switchbacking road past traditional villages, with lovely views thoughout. You'll reach Bhaktapur after 18 km and if you leave early you'll have time to explore this old capital of Kathmandu. You can make a great bike trip from Kathmandu to Nagarkot, down to Changu Narayan along a dirt track and then back to Kathmandu partly on back roads and the rest on paved roads. Only try this on Saturday, when there is slightly less traffic!
Nagarkot & Panauti
Panauti, a village noted for its numerous temples with magnificent woodcarving is a great ride from Nagarkot, dropping down on dirt roads to the south of Nagarkot viewpoint. Passing the highway at Banepa, continue along a small, scenic road to Panauti and then return to Kathmandu via either the highway or backroads north of the highway.
Dakshinkali & Chobhar
A great Saturday ride from Kathmandu, Dakshinkali is located 22 km from the city center on the southern rim of the valley, past Pharping Gompa and village. The shrine, dedicated to the fierce goddess Kali, is especially crowded on Tuesdays and Saturdays when animal sacrifices are offered to the deity. The ride is all on-road but the roads are small and offer plenty of great views, even views of the surrounding Himalayan ranges when the weather is clear.
RAFTING, KAYAKING, BUNGY, CANYON SWINGS & CANYONING
(adventure)
The Last Resort
Near the border of Tibet ...
Borderlands Eco Adventure Resort
Near the border of Tibet ...
Royal Beach Camp
Near the border of Tibet ...
***
PARAGLIDING, ULTRALIGHT & MOUNTAIN FLIGHTS
Frontiers Paragliding
Pokhara
Sunrise Paragliding
Pokhara
Pokhara Paragliding
Pokhara
***
ROCK CLIMBING
Nagarjun Forest
Shivapuri National Park