Each city has its beacon to tourists—be it the Empire State Building or the Acropolis, the Blue Lagoon or La Sagrada Familia—and it's hard to resist its pull. We've all had this moment, when we ask ourselves, Should I really wait in line for the experience? Will I have lifelong FOMO if I do? At Traveler, we debate these attractions all the time, and here, we offer the ones that left a lasting impression, even after a two-hour queue.