I tried using Special:Nearby in my local instance and it didn't work. I wasn't able to find any documentation on how to set it up. I figured out that you had to set the $wgMFNearby global to true in order for the special page to load. (I added this to https://www.mediawiki.org/wiki/Extension:MobileFrontend#Configuration_settings). Of course it still doesn't do anything besides load an empty page though. How do you make a page's geodata discoverable to Special:Nearby? Do I need to install Extension:GeoData? However it works, we should document it so other people can set it up easily.