There's a lot of marketplaces where you could promote the app to avid travelers. I work mostly in the travel space, and building an audience is always the hardest part, especially since there's so much competition.

You have two great options, and the first I'd say is to create a press release.

You can get listed on a wide variety of networks and get media exposure and brand awareness to start boosting your user base. For all of those new users, implement a follow-up strategy that encourages them to become paid users within 2 weeks.

Happy to chat further!