I tried several plugins and no one was able to load (inside the popup) the web page I wanted i.e. http://www.nicovon.joomlafree.it/sala_camino.html
this testing site is, instead, the site where I'm doing these tests. by clicking on the link at the bottom (Click on me!) or by clicking on the first photo, should open (inside a popup), the web page that I wrote in the link above.
Update. the pop-up appears to be widening to the correct size, it does not close, but is white.