You can make the trek through Gosainkund in either direction combined with a trek to Helambu or Langatang. It is also a worthwhile seven or eight day trek in its own right. There is a strict ban on the use of firewood in Gosainkund, so if you are camping, be sure to bring kerosene for fuel. The route I have described is from Dhunhe of Syabrun to Tharepati. From Tharepati, you can either continue to Helambu or go directly back to Kathmandu.