Getting to Koshirakura is an adventure in itself.
From Tokyo take the Jyoetsu Shinkansen (Shinkansen stands for bullet train) to Echigoyuzawa. In Echigoyuzawa change trains to the *local* Hokuhoku line to Tokamachi. Make sure you don’t take the Shinkansen again! Also, double-check that the train you get into stops at Tokamachi, some of the express trains skip this stop.
Once in Tokamachi take the East Exit from the station. There’s a small tobacco shop in the plaza and right in front of it is the bus station (a bench and a sign). The bus to Koshirakura departs three times a day only, one around 12:50, the second one at 4:00 pm, and the last one at 6 pm. The people at the station and at the tobacco shop speak some English so they will be able to help and confirm the schedule. Koshirakura is the last stop of the bus and most likely the bus driver will leave you right in front of the school building, where the workshop happens.
In the map below you will find instructions for driving from Narita Airport as well as the points of the train stations previously explained.