There's also this, not from the original Arabian Nights but from European sequels in the same style:
https://en.wikipedia.org/wiki/Domdaniel
Quote:
Domdaniel is a fictional cavernous hall at the bottom of the ocean where evil magicians, spirits, and gnomes meet.
Overview
Domdaniel was first mentioned in the continued story of the Arabian Nights by Dom Chaves and Cazotte (1788-1793). It was described as being located in the sea near Tunis. In this hall, the ruler Zatanai held his court, which included the magician Maugraby and his students.
Robert Southey later used Domdaniel in his multi-volume oriental poem Thalaba the Destroyer (1797). The hero of Southey's story, Thalaba, is the son of Hodeirah and the last surviving member of his family. It had been prophesied that the spirits of the Domdaniel were destined to be destroyed by a member of that family, so they sought to put an end to it.
One of the magicians named by Southey as dwelling in Domdaniel was Abdaldar. He was selected by lot to hunt down Thalaba and slay him. But the youth Thalaba accomplishes the destruction of the magicians in the final volume of the poem despite their efforts to kill him and his surviving family.
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I haven't read either of these, but there might be something useful there, you could check. Even if Domdaniel isn't itself full of water, and it might be, there might be something about them getting there. A search suggests that they're both available online.