You pose a good point, but if it was made as a torture chamber, what of the well back in the village? This too was made by the shiekah and it holds the same basic design, mysterious and deathly, but this instead was made to seal the spirit bongo bongo.
Also, if it was indeed a -temple- of shadows, as in somewhere of high importance or dignity, why not use the well to torture the prisoners or somewhere else that may not be as -holy- I guess you could say.

Which brings a thought, does anybody know just how old the temples, or the well, are?