The Tower of Penitence serves as a prison for those awaiting execution under the powerful Soukyoku (its the name of the execution grounds). The Tower is heavily guarded, and within it are contained very slim windows for the sole purposes of the prisoners to gaze at Soukyoku before their execution.
The sewers are like a complex maze that twist and turn. It is likely that if you don’t know your way you’ll easily get lost. The 4th Division is the only division that can easily navigate the labyrinth as they use it as a supply route to get from one are to the next easily. On top of that the sewers are quite clean seeing as how the 4th Division only deals with the “chores” of The Sereitei.