It appears that those searching for a serene vacation might want to steer clear of certain hotspots - as a travel expert has recently revealed a list of European destinations that become unbearably crowded during the summer months. The seasoned traveller has warned about the overwhelming numbers of tourists swamping some of the continent's most beloved sites. Even the world-renowned cities like Barcelona have resorted to hiking up tourist taxes in an effort to deal with the influx of visitors.