Choosing any research topic is always challenging. In this assignment you're choosing your travel/vacation destination. If you do not have an idea, trying brainstorming based on what interest you, what you would like to learn about, and how adventurous you're feeling.
As a reminder, an informative speech provides information about a specific subject to an audience. The aim of an informative speech is to help your audience to understand and to remember the information you are presenting.