As one of the top-tourist-destinations, I’m not sure if Schönbrunn qualifies as a secret insider tip (hint: it does not). Still it is one of those sights you just cannot miss when you come to this city – not only is it astonishingly beautiful, it also has something to offer for every desire and budget.
First, there is the palace itself, so if you're into history or kitsch, you should go take a tour. If you’re more the outdoor kind of person feel free to enjoy an imperial walk around the extensive park with amazing fountains, beautiful alleys, the rose gardens or the Gloriette with its impressive view over the area – all for free!
Walk up to the Gloriette, sit on the grass (ignoring the signs telling you not to), and enjoy the view of the gardens, the palace and the whole city.