I planned of so manythings when I went this December.....  didnt got time for anything... Add these two to your list.....
Fresh Water Swimming at Kirtipur,
Go Karting at Manamaiju (Balaju) .... nice track (Dont know if they still operate)

The best thing  had while my visit to Nepal this time is.....
Kakani ko rainbow trout machha..... Its great... Fresh fish caught and prepared after you order....
Loved that... dont miss it...