I am familiar with Montjuic, and a few similar cruising grounds in Spain.
What keeps them alive and kicking is the sheer number of their gay patrons. You go to MJ or any other big and popular cruising ground knowing that you have good chances to hook up and have sex. You also know that you won't be alone, stuck on a trail with one or two guys who you may care as little about as they do about you. You know that you may see familiar faces; people whom you know well, or even guys who always nod with their heads when they see you because they know you 'from seeing'.
The Apps, Internet, Craig & Co. destroyed small, less popular cruising sites, theaters, smaller spas, quite a few clubs and bars, too.
Just like the use of Apps, cruising in public parks is perceived to be free of charge. This is a very significant part of their charm, especially in a country like Spain which is still having record numbers of unemployed people. If there is no direct, out of pocket expense, people are more tolerant when it comes to the conditions of use and the possible failure to get what they were hoping to get.
It is also true that public park cruising scores big time over the Apps on at least two counts.
First off, more and more folks are realizing that the apps show the pix that may be 10 or more years old. The stats shown are still using the old AOL M2M chat rooms' measurement system that had an 8 incher as the least you could offer to an interested bottom, who usually portrayed himself as a vers top
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Second off, the Apps are meant to foster communication. Good in itself, communication is not what each and every man wants. A few are happy to unload, or get some action and move on... The apps do not really work for them that well.
KD