One of the interesting features of Maiden Tower structure in Baku is its construction of well. The well with 0.7 m diameter is inside the south-eastern wall. Calculations have shown that, the well has nothing to do with the level of sea water. The well water was chemically analysed, its being fully fit for drinking, determined. The well gob begins from the level of the third floor and lasts 13 meters down along the wall. It was concealed in the Tower wall to ensure the safety of the well.