White Lodge
Now we know what White Lodge looks like. It's a fortress on an island in the middle of the ocean.
When Cooper was trying to find his way out of the Black Lodge, at one point he was standing on a balcony overviewing the ocean (right before he entered the room with a girl with no eyes)... now we know that he was in a White Lodge. Also, the moment before he ended up on a balcony, he was in that glass box. Looks like the box is a transition point between two Lodges.
This fits the story that Hawk (or Briggs, can't remember which one) once told about the Lodges - if you want to get into the White Lodge, you have to go through the Black Lodge first. And apparently, (only?) from the White Lodge you can return into the real world.