Travelling 2nd time to japan

Hello everyone, its my second time going to japan. My last trip was about 14 days, I visited Tokyo, Kioto , Osaka, Nikko, Nara and Hiroshima.
This time im going to travel with my gf and is her firts time there, i dont have any trouble coming back to that citys but i would like to go another places new. We are going to spend maybe 21 days, im looking for some recomendations

by TulioR26