Forums usually work best on sites that already receive thousands of visitors a day. Lots of people visit and read forums without taking part. Unless you're very fortunate, you might need at least 2,000 visitors a day to make one work well.
It helps to have a good-sized mailing list, too, in which you can announce your newsletter and remind people that your forum exists.
You could try promoting your forum more prominently on your main page,
perhaps quoting snippets from controversial posts.
Perhaps you have some friends interested in travel who would be willing to start a few controversial discussions on your forum to build up a bit of interest. Otherwise, people are likely to have a quick look and leave without taking part.
You're going to have to think about buzz marketing and getting people talking about you.