Cistern in The Ragged Flagon in Riften, appears on a shelf behind the desk after completing 35 Thieves Guild jobs. When using Destroy the Thieves Guild, it will instead be in Belethor's General Goods in Whiterun, where it can either be bought or stolen.

Normal Location

The Ragged Flagon in Riften

Destroy the Thieves Guild Location

Belethor's General Goods in Whiterun

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