He plays the piano!
In addition to being one of the greatest sportsmen of all time, and a good swimmer, the fit Federer also has musical pursuits! He took up the piano as a youngster and is said to continue to play it to this day.
He has also shown his proficiency at playing the flute, most notably at the Lucerne festival.
He also plays the violin – as he exhibited at the Lucerne Festival
That said, fun fact – tennis player Daniela Hantuchova is a trained concert pianist!