Here is the full list of all 18 Le Château achievements.
Place a rock on a 1 tile world. Not sure why you'd do this, though.
Create a home for the loneliest person on the planet on a 1 tile world (looks cozy, though)
Finish a build on a 1 tile world
You built your first kingdom!
Fill a world with no castle objects at all
Fill world with no nature whatsoever (3x or bigger)
Have 3 or more houses in your build
Fill every tile on a 3x3 world or bigger with water
Have more cavalry than houses in your world
Finish a build with only 1 object in a 5x5 world or bigger
Finish a build in a 5x5 world or bigger with no food related tiles
Fill a 3 tile world completely
Fill a 5 tile world completely
Fill a 7 tile world completely
Fill a 9 tile world completely
Fill every tile on an 11x11 world
Unlock every tile
Fill the outside of a 5x5 world or bigger with only castle objects