Tendril of Corruption

The Tendril of Corruption is a section of the massive body of N'Zoth resembling a giant sea monster similar to Iso'rath. Uu'nat is fought in its eye-filled bowels.

The Shrine of Shadows is eaten by a maw of the Tendril of Corruption opening the way inside the Tendril of Corruption.

Speculation
Taking into consideration that in the in-game map you go westward once you fall through the Shrine of Shadows into the Tendril of Corruption, it is possible you are parallel the Blessed Path and that the room with Uu'nat and N'Zoth's eye is thus directly below the Fonts of Cleansing, which the second Tidesage mural depicts tentacles shrinking away as the Tidesage pours glowing water on another Tidesage.