A user by the name of Sklo on the Polish forum for Pokemon Polska has possibly discovered a previously uncovered part of Isshu called the ‘United Tower’. He took multiple screenshots of it which I’ve put behind the spoiler. Unfortunately there is not much information known about this location but it does feature the NPCs that are responsible for WiFi trading/battling at the desk so I would assume that it has something to do with WiFi features. The two screenshots simply tell the player to come over this way and the other is an NPC saying he hasn’t seen your face before so this must be your first time here. The user posted that his camera has the date wrong, so please ignore that. This location may have been accessed via hacking methods so we are not yet sure you can go to it during normal gameplay.
ps- Thank you GlossyGem for the tip! Always good to have Polish visitors xD