trefaes saidDoes anybody has experience with nudity in gym...meaning training naked with other guys?
The only places I know are upscale bathhouses. One I've used has equipment & space as good as any ordinary gym (link below with pics, and they are a US chain, so explore their other locations).
I think few guys use it as a primary workout place, but you certainly could. The dress etiquette can vary by the guys there, but total nudity is permissible and does occur, though not mandatory. Like any gym, the only requirement is that bare skin not touch the equipment, so you deploy towels.
Some guys will wear nothing but a jock, especially when using equipment like the treadmill where you're jogging, since your unsecured stuff can feel awkward. (though not unpleasant for a spectator to watch
If there are any nude gyms that are strictly that, and not associated with the other aspects of a gay bathhouse, I'm not aware of them in the US. If you remain in Spain, I can ask my friend's BF, who is originally from Seville and returns there frequently.http://www.the-clubs.com/photos.cfm?location=FtLauderdale
Be sure to browse the photos. Nice bathhouse, my favorite.