I don’t remember what this pool was used for, but it’s located on the lower level near the ablutions room and fountains.

“With a prayer hall that can accommodate 25.000, the Hassan II Mosque is the second-largest religious building in the world, after the mosque in Mecca. The complex covers 9 hectares (978,774 square feet), two-thirds of it being built over the sea. The minaret, the lighthouse of Islam, is 200 m (656 feet) high, and two laser beams, reaching over a distance of 30 km (18.5 miles) shine in the direction of Mecca. The building was designed by Michel Pinseau, 35,000 craftsmen worked on it, and it opened in 1993. … [It] is a monument to Moroccan architectural virtuosity and craftsmanship.” (“Eyewitness Travel, Morocco”)

A fountain in the ablutions room, posted earlier: