Where did the doors come from?

[Rozza_17]

I'm currently reading the series for the second time and my old questions are re-surfacing.
Is there an explanation for how the doors got there? I know why they're there but I would like to know how and who put them there. Any theories?

[GNTLGNT]

Pella....

[bluesology]

I'm guessing here but I remember at some point the possibility came up that Walter was responsible for putting Eddie, Susannah and Jake into Roland's path in order to slow him down or throw him off his quest. Considering Walter's tarot reading for Roland at the end of Gunslinger, it's possible that he put the doors there.

I suppose that it is also possible that whatever entity resides at the top of the tower put the doors and subsequently Roland's Ka-Tet into his path in order to provide him with allies.