I printed the map using a poster/plotter printer in two sections that I split up in photo shop, scaling the map size and resolution to fit a 1in player grid (the grid marks are there, but faint).
I then taped 12 2ft×2.5ft foamcore boards together and glued down the map, using gluesticks for the majority and hot glue to keep the edges down. I taped it so that it is a trifold, condensing down to a single 7ft×21in panel for storage and transport.
Someone else here in the comments suggested cottons balls for fog of war, so I am gonna get those and some poster tack to keep it all vertical. I am gonna track their progress by making player tokens and using poster tack to keep them on the board.
The map is on paper, using a poster/plotter printer I have access to through work, and the backing is foamboard. Only $40 in materials all said and done.
The reason I did it was because the group wanted a world map poster of my homebrew setting to put up on the wall, but I am not a skilled enough artist to make it look nice enough. Professional, pre made maps ARE withing my skillset to make a massive poster from.
I had been struggling with figuring that out, but cotton balls with a bit of poster tack to keep them attached will be perfect! Thanks for the idea. I was going to do black cardstock with each room cut out, but your suggestion is 1,000,000× easier
My thought was to make player tokens and use poster tack to move them around as they explore, keeping it all vertical.
I just finished it this morning at 2:30, so I still haven't worked everything out, but the first reveal will be today, even if I don't think they will start using it today.