We highly recommend AVOIDING the Magic Fountains on a Thursday night, at least for the first show (9:30 p.m. in early August). The Fountains do not have a show on Monday, Tuesday or Wednesday, so Thursday night is hugely popular. It was incredibly crowded. There were tens of thousands of spectators, perhaps more than 50,000, maybe even 100,000. And there was no security. Forget about terrorism, we were concerned about being crushed in a stampede. It was nearly impossible to leave early because there were no paths through the dense crowds on the stairways or sidewalks. It's a good show, and well worth attending, but go later or on another day. (Note: it is possible that it is just as crowded on the weekend. Hopefully, others will provide guidance on that.)
There is physically no space for such large numbers... there are less than 10,000 people on those exceptional days in which it's really crowded. In any case, an open space like that allows nearly 360º for escape routes, so there's much less danger in a hypothetical stampede there than in almost any other enclosed space (a stadium, etc)
All activities, public or private, are regulated and have to comply with the City Charter and Code of Ordinances in matters of security, health-risks and fire prevention among other requirements, be a concert, a football game or a street parade. The Magic Fountain is a public event, for which the City Hall is directly responsible.
The site is full of police, mostly in plain clothes although some uniformed patrols are also stationed nearby. Also, less than 200 yards from there so it happens to be the HQ of the Guardia Urbana (City Police) for that district in a street that's appropriately named "City Police Street"!!! and at 400 yards, at the other side of Plaça Espanya, one of the main offices of Mossos d'Esquadra -the equivalent to your State Police.
Maybe in your neck of the woods the presence of heavy-armed GI Joe-type police suits your society....well, not over here, policing is generally discreet and not menacing, and that's the way we prefer it. In any case, go ahead, start an incident anywhere in the city, especially those sites with more crowds, and you'll see how fast you have several patrol cars surrounding you. Not seen doesn't mean they're not there.
A final reflection... this country has quite successfully battled terrorism (ETA, GAL...) on and off since the mid 1960s? This city regularly organises large events, be international congresses like the World Mobile Congress, high-risk sports events like football matches among two of the most followed teams in the World or international championships in many other sports, cultural gatherings and folk celebrations like La Mercè with over 2 million attendees or Festes de Gràcia (1.8 million), Barcelona receives 12 million tourists every year (the city population is 1.8 million), and she held the Olympics in 1992... do you really think things are not thoroughly planned and coordinated even if it doesn't look like so to the casual eye? Again: not seen doesn't mean not there.
Not sure why your response is so hostile. My primary point is that the area surrounding the fountains is incredibly crowded. Definitely more than 10,000 people. As I noted, we could not leave early, because the stairways and sidewalk back to the Metro were packed with people, and there was no open path until we got to the street. I was not concerned about terrorism. I was concerned about simply being able to move from Point A to Point B on an open path. I have attended very large cultural and sporting events, and public and/or private security is usually deployed to ensure that there are open paths for walking and emergency vehicles. I will note that the STREETS were kept open for walking and/or emergency vehicles, but from where we were watching the fountains, it was 1/2 km to the nearest street.
Being hostile was not my intention... straightening facts and reassuring other readers it was indeed. I will not deny that it's very crowded and that for some can be uncomfortable, I often try to avoid crowds myself too, but a post like this might unnecessary cause the wrong impression, so it's best to have more background and let everybody draw their own conclusions and act accordingly.
Fair enough. I will say again that "it's a good show, and well worth attending." I encourage people to go. And I encourage everyone to go to Barcelona, which is a terrific city. Your "final reflection -- do you really think you'll show granny how to suck eggs" comes off as rather hostile. As you said, let's stick to the facts. I enjoyed our discussion and hope that others can benefit from it. And thanks to Rick Steves for hosting this open forum.
Granted, maybe the wrong choice of words. I just corrected it.
During La Mercè Festival in Sept every year there's a pyro musical show in this location to close the festival. A large display of fireworks, music and light... this is a picture of last year. That was 140,000 attendees and you can only see an angle in this image. I hope you can see the difference with a regular Font Màgica show any day during summer.