The Eiffel Tower is about 15 centimetres taller in summer than in winter.
The tower is made of iron, and metal expands when it is heated. On a hot day the sun-facing side expands more than the shaded side, so the top also leans slightly away from the Sun.
Why is this true?
Thermal expansion is why bridges have expansion joints and why railway tracks used to be laid with small gaps. Engineers have to design every large metal structure to breathe with the seasons.
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More about science & nature
Science and nature supply facts that feel like they break the rules until you see the mechanism. Hot water freezing before cold, glass that flows, lightning hotter than the surface of the Sun. Each entry keeps the physics or chemistry short and readable, states plainly where the effect is still debated, and links to a source for anyone who wants the full derivation rather than the headline.