A winding stone staircase leads to the main plaza above the Hall. The wall is studded with these yawning lion's heads, part of the ingenious water catchment system that Gaudí designed. Originally, rain that hit the main terrace was directed to and through the stone columns below where it would feed and power the fountains. Given that the average annual rainfall in Barcelona is only about 23 inches, I don't think the fountains would have been terribly lively.
For an even better view of Barcelona, trek up the hill to las tres cruces. There is no guard rail on the narrow stair, so hug the center as you ascend, and especially when descending! From the top, you and 30 of your newest friends will have a 360-degree panoramic view of the city.