Undead Settlement sewer entry?

[brandtex]

I have wandered the settlement for a long time without finding a way into the sewers. Searching the forum has not helped either. The door by the big rat is locked and the door to the cell by the dude with the big hammer cannot be opened from that side.
So how the devil do I get in there ?

[KaRtoON]

to enter the door next to the big rat basically u need to pick up some ashes in the area where the giant shoots the arrow, give those to the handmaid an she will now sell you the grave key wich opens that door

[brandtex]

Thanks for your help! Just after writing, I found those ashes and I have the key now .. finally