Hearthhome.

So if you look on the new map of Runeterra, you can see that Hearthhome is not marked anywhere on the map in the Freljord. And it’d be easy to spot a massive active caldera even if it wasn’t labeled. Above the Freljord across the massive river is another glacial continent that has a small area labeled “The Ursine Lands”. I think that Hearthhome may be in this currently unviewable area, north of The Ursine Lands.