It doesn´t always have to be treasures or traps. You also can build secret stairs and passages.
Most suitable to build a secret passage is Module 8 due to its thickness of 4 cm.
Use a cutter-knife to cut vertical into the gaps between the floortiles and release a block of three tiles.
Mark the cutting lines and release those two tiles which will cover the stair later.
The covering tiles should be as thick as the stairsteps. I choose 0.5 cm. Now release a block with the remaining, third floortile. But don´t cut off the floor of our hidden passage.
Now you can remove slice by slice so that the stairsteps evolve from the the remaining block.
Use a ballpen to press the gaps of the floortiles and stairsteps into the material.
Mark an archway onto the released block with the third floortile and break it rough out of the material by useing the cutterknife (Don´t throw the removed pieces away).
Now glue the archway back into its former position into the module.
Cut two small angles out of the removed pieces of the archway and glue them in front of the stony arch. Those angles serve for holders for the covering tiles.
With the covering tiles in their position it looks like that from the bottomside:
Now paint the stairs and the archway. You can also paint the floor and the walls of the secret passage.
It´s done very quickly by drybrushing the parts.
You can glue the staircase back into its former position into the module afterwards.
At least you can drybrush the rest of the module and the secret passage will be hidden.
We wish you a lot of fun with constructing and painting.