You Can Get There From Here
Okay, so by looking at the Barcelona metro map, you note many places in which the metro lines overlap. "Great," you think, "I can easily change from line 1 to line 2 here, no prob." Heh heh heh... suuuuuure you can, if you don't mind walking seemingly a kilometer or two through long and sometimes windy passages connecting the supposedly linked metro lines. No wonder why all the Spanish people are thin!