Yesterday, Platonides wrote: 
Several people have asked me for a way to view the most photographed
monuments.

This tool is now implemented
http://toolserver.org/~platonides/wlm/monuments.php

The most photographed monument from all countries* is Colombian 06-050,
with more than 2000 photos. Although that identifier spans the old sector of the
city of Tunja, so it's not really fair to compare it with 'conventional monuments' with
are a statue or a building.

As counting the number of photographs gives too weight to a big uploaders (single users sending
hundreds of photos of the same monument) and large monuments (those where you take a lot
of photos eg. Versailles > Eiffel Tower), I implemented a second mode, using instead the number of
photographers.
And the worldwide winner is... Indian Monument N-UP-A28-a, also known as Taj Mahal, of which
114 different users uploaded a photo in Wiki Loves Monuments 2012.