The Quartz skin (which you can select in your preferences) include a breadcrumbs feature beneath the search box that helps you to navigate around Wikia and find interesting wikis on a topic related to the one you are browsing.
For instance, the Star Wars wiki has a breadcrumb trail that looks like this:
The first link takes you to the home page of Wikia.
The middle link will take you to a Wikia hub where you can find more wikis in the same subject area.
The last link, which displays the wiki's title, will take you to the main page of the current wiki.
The hubs for existing wikis were chosen based on the primary category that was assigned on the wiki's description page on the Central Wikia. New wikis will be assigned to a hub on creation.
How do I change the hub my wiki is assigned to?Edit
Currently, there is no manual way for you to change your hub assignment, but if you feel your wiki would be a better fit in a different one, you can leave a message about it on the wikia:Help talk:Breadcrumbs.