Islands only link up every once in a while, so once you land on an island that's it at least for now. When islands link up you'll see a big '?' appear in the page header that you can click on to explore the linked island. There are two islands right now because the populations are low. There's a mechanism for discovering new islands as the island populations grow.

My hope is that by smooshing people together randomly and making it harder to move, people will have a new way (new old way?) of interacting online that has more of the good aspects of offline socialising. But you're 100% right that without a reason to engage it's going to be very quiet. I'm looking at different ways to tackle this that range from "it's a video game now" to something much more subtle.