Since 2008, the number of tourists visiting European countries rose incredibly (http://bit.ly/2BHOCDt). Obviously, this steep increase in numbers had consequences and not always positive. For instance, certain locations (e.g. Barcelona, Venice Amsterdam and Rejkjavik) are suffering from a strong tourism overcrowding. What do you think is the main challenge that this steep increase brings for cities (e.g. Venice and Barcelona) targeted by mass tourism?