@juliohm kindly showed me how to do it.
grid = CartesianGrid(1,1,1)
boundary(grid[1])
6 SimpleMesh{3,Float64}
8 vertices
└─Point(0.0, 0.0, 0.0)
└─Point(1.0, 0.0, 0.0)
└─Point(1.0, 1.0, 0.0)
└─Point(0.0, 1.0, 0.0)
└─Point(0.0, 0.0, 1.0)
└─Point(1.0, 0.0, 1.0)
└─Point(1.0, 1.0, 1.0)
└─Point(0.0, 1.0, 1.0)
6 elements
└─Quadrangle(4, 3, 2, 1)
└─Quadrangle(6, 5, 1, 2)
└─Quadrangle(3, 7, 6, 2)
└─Quadrangle(4, 8, 7, 3)
└─Quadrangle(1, 5, 8, 4)
└─Quadrangle(6, 7, 8, 5)
I knew it was there, I just couldn’t find it!
Kind regards