The Eiffel Tower grows about six inches taller in summer.

The Eiffel Tower’s iron structure expands when heated, and on hot summer days the tower can stand roughly 15 centimeters, or about six inches, taller than it does in the depths of winter. Iron expands predictably as its temperature rises, and with a structure over 300 meters tall, even a small amount of expansion per section adds up across the whole frame.

The tower also leans slightly away from the sun as the metal on the sun-facing side warms and expands faster than the shaded side, shifting the very top by several centimeters over the course of a day. Gustave Eiffel’s original design, built for the 1889 World’s Fair, accounted for this kind of thermal movement, along with wind sway, which is why the tower has remained structurally sound for more than 130 years.