Create some feature walls with window-openings to break the endless walls. Maybe your adventurers will see something through them?

Remix of Devon Jones' Cut Stone series.
With the Openlock triplex base you can click the tiles together in a limitless configuration of your choice.

I added aditional beams, because I found that printing the big ones without them gives a very bad texture at the bottom. And if I put the time and money in tiles, I want them to be pretty and sturdy.

Instructions:

• Print the tiles of your choice.
• Remove the small supporting pins on the sides.
• Print Openlock clips to connect the tiles.
• Push one or more Openlock clips into the tiles (depending on the size of the tile 1 can be enough, 2 works best with big tiles).
• Connect the tiles together.

Making your own (Cut Stone) castle/dungeon/map? Try these components:

• Celtic Knotwork cut stone tile
• Pillars
• Alcove
• Walls with windows
• Grate tile
• Stairs
• Broken Wall

Yandalf posted some of the other parts already.