I've always wanted to create a huge travel portal with loads of content but never had the time really.
This will probably set you back a bit of money and a fair bit of time before you really see any profits in return, so you may want to skip this idea if that’s a problem.
Think of this like a Fiveminuteguide.com site but purely about travel. Travel keywords always pay well with adsense and while the competition can be fierce for hotly contested phrases and keywords, there are thousands of little keywords you can target as well.
My dream was to have a mini guide for every destination in the world, and while this would probably take me years to compile, I would then have one of the largest content sites on travel on the Internet, so the rewards are there.
There are many ways you can do this business idea, it just depends on how much time you have to spend on one project.