The Cooling Tower is also the most recognizable part of a nuclear power plant. The actual fission of atoms and generation of power generally takes place in an unassuming building next to these impressive hyperbolic concrete structures. They look like tall cylinders with the middle cinched inwards.
More generally cooling towers remove heat from water by evaporation for industrial facilities and commercial buildings. The coolant water is moved across a fill media of some variety to spread it out across a very large area, maximizing the surface area exposed to the open air. To reduce the space required the fill material surround a wooden or fiberglass framework in inside the tower.
In a counterflow system the air inside rises as it gets warm and is replaced by cool dry air flowing in the bottom of the tower. Meanwhile the remaining water is cool and is collected in a basin to be recalculated by into the operation or power plant. Sometimes the towers can have recalculation problems, where warm air leaving the tower cools rapidly and plunges back inside the tower. Such air is already saturated by water and so reduces the efficiency of the cooling unit. This is the reason that the cooling towers of nuclear power plants are so large. Their height is such that the structure acts like a chimney, catching the wind causing the air to be drawn out from inside the tower. In smaller towers usually a fan is added to smaller towers to keep the air moving in the proper direction.