Considering that this could be a wide range of things. I'd have to ask a few questions..
1. Has the ad been clicked in the past, if so what is the CTR
2. If not, then have you tried different text on the ad copy, if so, how many times a week did you try it.
3. How many times has your ad ever been shown?
There's also a diagnostics tool that's new when your viewing the campaign. Might also want to try that.
Could just be a bug too.
Being that it's Travel.. that's highly competitive. See what others that are in your niche are buying for keywords
SpyFu
It can be frustrating but once you hit the sweet spot of the web the clicks come in like crazy
Good luck!
Snerdey