WAW is walkable, but I don't know if people want to do it. On foot, the airport is about an hour from my dormitory (near Pole Mokotowskie, just outside the city center), and the center proper should be about another 20-30 minutes on foot.

Some airports in the Philippines are walkable too: examples I can think of are MRQ (Marinduque), CGM (Camiguin) and even MPH (Malay/Boracay).

Also, if I'm not mistaken, I saw some bike paths near PRG.