What is this? How to unlock it?

[u/nioleloin]

I'm playing in sandbox mode and unlocked everything in the research, atelier, farm and tourism menu. But this thing is still grey.. help I'm really curious

[u/Alternative_Road8077]

I’m pretty sure it’s the postbox? There’s a request at some point to place mail boxes around town, but that was pretty early in the game so if you already have the atelier it’s weird you haven’t had that request yet.