Achill Island is home to the Highest Sea Cliffs in Western Europe.  They are 668m tall, on the northwestern face of Croaghaun Mountain in Dooagh, and can only be seen from the sea, the air, or the top!  In fact, they're actually behind the peak that you can see in this picture, and drop straight into the Atlantic Ocean below.  When you're on top of Croaghaun sometimes you can't even hear the waves beneath; they're so far away!