At least that's assuming that you'll want to visit at quiet periods. If you expanded to include pubs and clubs, popularity might be more desirable.
Perhaps change the graphs instead of being block colour to have a texture of little people - eg something like http://static2.bigstockphoto.com/thumbs/9/8/7/large2/789645.... or http://www.vectorstock.com/composite/49471/statistics-graph-...
edit: also, why can't I search or see a full list of all places?
edit: Also for SEO you should change the URL to something keyword-packed like whenshouldivisit.iamdanw.com/when-is-british-museum-busy and offer alias short links like whenshouldivisit.iamdanw.com/british-museum, etc.