Kakani is (so far) the closest possible bouldering area near Kathmandu. It is still in the making of and in need of route cleaning and developing. Approach is a slippery and steep downhill. Ask directions and company from Astrek Climbing Wall in Thamel (http://www.astrekclimbingwall.com/).
Looking to scrub some moss, stumble through a thorny jungle and get a FA? Well this is the place for you... that is if you have some time to kill in between treks or during your busy life in Kathmandu. It is unclear how much rock is in the discovered area but it looks as though there will be a few multi-pitch routes as well as numerous boulder problems in the coming years. Like all places in Nepal the routes will be bolted but that might prove to be a challenge as the sandstone tends to be a little weak in some areas (so climb with the intention of flashing or you might loose crucial foot holds if you repeat attempts.)