The Eiffel Tower grows 15 cm taller every summer

Iron expands when heated, so the Eiffel Tower — made of 7,300 tonnes of wrought iron — grows roughly 15 centimetres in height on the hottest summer days compared to winter. The same thermal expansion also causes the top of the tower to lean slightly away from the sun on hot days. Gustave Eiffel designed it with this expansion in mind.

Source: Eiffel Tower Official Technical Documentation; Thermal Expansion of Structural Steel, ECCS (2006)