WordNet (r) 3.0 (2006):

bleachers
    n 1: an outdoor grandstand without a roof; patrons are exposed
         to the sun as linens are when they are bleached

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "bleachers":
   Texas tower, beacon, belvedere, bridge, conning tower, gallery,
   gazebo, grandstand, lighthouse, lookout, loophole,
   observation post, observatory, outlook, overlook, peanut gallery,
   peephole, pharos, ringside, ringside seat, sighthole, top gallery,
   tower, watchtower