Abstract: A cooling tower for condensing water has a hyperbolical main wall with an per portion which defines a passage for ascending vapor-laden air. The upper portion contains an annular insert serving to intercept currents of cool air which develop and tend to flow into the interior of the intermediate portion of the main wall at low wind velocities and/or to intercept turbulent air which develops and tends to flow into the intermediate portion when the wind velocity at the top of the tower is high. The insert may constitute a sheltered passageway for workmen and may be made integral with the upper portion of the main wall. The width of the annular space which is defined by the insert and upper portion of the main wall may be a whole multiple of the depth of such space, and the cross-sectional area of this space can approach one-half the cross-sectional area of the passage through which cooling air escapes from the tower by flowing upwardly within and above the insert.