<http://schema.org/keywords>
"sky, city, street, travel, buildings, europe, tower, vacation, old, tourism, architecture, symbol, history, pavement, town, home, stone, luxembourg, palace, scenics, landmark, grand, medieval, houses, front, hour, destination, historic, european, touristic, echternach"^^<http://www.w3.org/2001/XMLSchema#string>
<https://marketplace.500px.com/photos/19552455/luxembourg-by-viktor-korostynski>