1_Way_Blocks is a mod that will allow you to see through walls, as well as make the block a 1-way portal.

This is done by un-hiding a texture that was removed from the painting atlas in the game.

It doesn't seem to affect gameplay much. It doesn't affect frame rates like CCTV cameras do. It is a simple and short code.

The way this works is by joining the game and making a paint brush. You can then select the DRYWALL TAN BASEBOARD texture as shown in the image. You can now paint the block you wish to make transparent. This is a permanent effect. You cannot erase it once painted.