Make a 2d menger sponge
SOGL V0.12, 19 bytes
1¹.{³³┼┼≥:10ŗ;┼┼⁴++

Try it Here!
1¹                   push [1]
  .{                 input times do
    ³³                 duplicate top of stack 4 times, resulting in 5 total copies in the stack
      ┼┼               join the last 3 copies horizontally together
        ≥              put the joined at the bottom of the stack
         :             duplicate top of stack again
          10ŗ          replace 1 with 0 only in the top item
             ;         swap the top 2 items
              ┼┼       join the top 3 items horizontally together
                ⁴      copy the item one below top of stack
                 ++    add together vertically