While Parisians were still hotly debating the aesthetic value of their newly erected Eiffel Tower, the Czechs decided that they liked it so much that they'd build their own version out of recycled railway tracks - which they duly did, in a lightning 31 days, for the 1891 Jubilee Exhibition. The tower's fiercest opponent was Adolf Hitler, who looked out of his room in the castle and immediately commanded his forces to remove 'that metal contraption'. Somehow, though, it survived.
The tower is fairly tatty these days, but the climb to the top is made worthwhile by phenomenal views of the city: more than just the usual vista of a set of spires poking over the top of the castle. Just try not to think about the way the tower sways in the wind.