Fencer, your idea of "Would you dare to win Espionage by capturing opponent's base without revealing it by a spy?" is good but rather easy. Just capture it with a sab! Perhaps modify the achievement to "Would you dare to win Espionage by capturing the opponent's base with a 4 or 5 without revealing it with a spy?"
(hide) If you only look at some of the discussion boards on a regular basis you can add them to your favourite boards list by going to the Board page and clicking "Add to my favourite boards". (pauloaguia) (show all tips)