The neutrino science center is located on Aobayama campus which is up on the hill. The physics building C is near the neutrino center, and it is best to go to the neutrino center first and ask. To get to the neutrino science center, it is safest to take a taxi.
Map of Aobayama campus.
Show this to the taxi driver.
Please see THIS, if you will come to Aobayama campus by bus.