'Knock Knock' began as the second half of 'Skipping Stones'. After crossing the lake, the contestants are faced with a wall that has four doors in it. One of the doors is real, but the others aren't.
The contestant has to run full-speed at a door. If it's made of paper they will burst through it and will have won the game; but if they choose a wrong door, which is solid, they will bounce straight off and lose. </span>
A second wall was then added behind the first. If a contestant makes it through the first wall, they then have to choose another door in the second wall. If they're lucky again, and they choose a paper door, they'll go through the wall and win; but if they choose wrong they won't get through, and they'll have lost.
The walls were then removed from 'Skipping Stones' and made into game of their own. The number of walls the contestants have to get through were doubled to four. Now they have to choose four paper doors, one in each wall, to make it all the way through and win.
This time not all the wrong doors are solid. Some are made from paper, but have a net fixed behind. If a contestant runs through one of these they'll be caught in the net and also lose the game.
If the contestants make it through the second wall they'll usually be confronted with the Boxing Monster (the Honey Monster in earlier episodes). They will need to make their way past him to continue on. If the contestants choose wrong this time they'll also end up getting a pummelling from the Monster.
Takeshi's Castle ThailandEdit
The row of doors has now increased to 7 making the game much harder than before. As added hindrances; behind some of the doors are water or mud pits.
In Episodes 10 & 68, coloured smoke bombs cloud vision of some of the doors.
In Episodes 14 & 74, Guards spray contestants with hoses to distract/hurry them.