This is actually a great tip you can use later on when it’s time to find topics to write about on your blog or site. When it’s time to create more niche sites it will become more and more difficult to find new topics to create sites about. Therefore I recommend you to find a couple of big boards where you can read through some of the most popular topics in your niche and create sites about them.
Big boards are easy to find, but if you would like some tips you could always use big-boards.com. Another good method to find topics later on are to search for “forum + your niche” on Google.
Search for your main niche
If your main niche is travel, you should visit travel forums to get more information about popular cities, etc. Then you could easily create a site for each city.