Doors would be a 2x1x1 vertical block, with a flat surface (No window, unlike vanilla doors) that blends in with other blocks. IE: A stone secret door has a stone texture. They could have a small distinguishing mark or symbol, as the walls one can use the move on in gen 3 did, or be completely blank and therefore difficult to find unless one knows where they are. Their location in the SP map if blank could be indicated by nearby terrain (Eg, a path of no long grass that cuts through a long grass patch and goes up to a flat cliff wall, a road that seemingly leads to a dead end, ect.) In multiplayer servers, they could be used to recreate the secret base system in minecraft, or used by players who wish to conceal the entrance to their homes from others.
Doors would be a 2x1x1 vertical block, with a flat surface (No window, unlike vanilla doors) that blends in with other blocks. IE: A stone secret door has a stone texture. They could have a small distinguishing mark or symbol, as the walls one can use the move on in gen 3 did, or be completely blank and therefore difficult to find unless one knows where they are. Their location in the SP map if blank could be indicated by nearby terrain (Eg, a path of no long grass that cuts through a long grass patch and goes up to a flat cliff wall, a road that seemingly leads to a dead end, ect.) In multiplayer servers, they could be used to recreate the secret base system in minecraft, or used by players who wish to conceal the entrance to their homes from others.