All the answers here! The main goal in 100 Doors is to escape the room. Using all the possibilities of the device you need to open each of 100 doors and move the doors to the next Level.
Search for hidden objects, solve puzzles and use an items to do this!
The sign on the door says big medium small small medium big.
Open the boxes on the left 321 then on the right 123.
The key will be in the 3rd box on the right