Petrinska rozhledna/Petrin lookout tower is Prague's so called smaller version of Paris' Eiffel tower. It was build in 1891. When the weather is right you can see places in the Czech republic that are more than 100km far away. There's a grand view on Prague Castle as well :)
The only drawback is that it is on the top of Petrin hill and you have to literally climb up here. But than again, there are those fabulous views on Prague during your climb.
Here's a link to the real Eiffel tower at Paris DP.