Boruto: Naruto Next Generations S01 E141 The Shinobi Prison: Hozuki Castle

Hozuki Castle is a prison run by the Hidden Grass, well known for being notoriously difficult to escape from. Boruto and Mitsuki are sent there to protect Kokuri, a former member of a brutal band of robbers known as the Mujina Gang who's now targeted by assassins after betraying and deserting the gang.