Deep down underground, I think about 50% of ads at tube stations are holiday related - white sandy beaches, sun etc. That should tell you how clever those advertising people are! On your way to work, during a horrible winter, on overcrowded trains(they sometimes don't even stop because they can't take more people on!!!) who wouldn't want to go overseas.
Imagine my surprise when I changed at Tottenham Court Road and they advertised Austria :)