Why locals love it?
The Petřín Watchtower offers the most beautiful view over all of Prague. Petřín is a miniature version of the famous Eiffel Tower, only a fifth of the height of the original. You don't need to climb the 299 stairs up the tower for a great view, the views from the surrounding gardens make getting to the top of the hill worth it.
Why you should visit it
Locals often stop by the statue of Karel Hynek Mácha, the Czech romantic poet and author of the famous love poem Máj("The May").His statue is a meeting place for lovers who come here on 1st May - the "Day of Love".
You can either walk or take a funicular.I recommend taking the funicular up (as the hill is quite steep) and then you can walk back downhill.