1. Go outside the château and press both buttons shown under "Next buttons". Button numbers refer to this top-view picture of the pillars.
  2. Check the dancefloor inside. If a light changed, click that square in the grid below - if nothing changed, click the X button.
  3. Click Submit. The "Next buttons" change.
  4. Repeat. After some rounds the labels beside each row and below each column fill in with the button that controls it.
  5. When only one button is left unknown the solver fills it in by itself and shows the finished mapping.

If you lose track (several lights on and no idea which buttons control them): click Reset, switch on Set manually, click every glowing cell you see on the floor, switch it off again and continue from step 1. In manual mode you can also edit the row/column labels and the "Next buttons" directly.

A light must only change after pressing both buttons. If one changes after a single press, the game probably missed one of your earlier presses and the mapping so far may be wrong - reset and set the state manually.

Solver
Next buttons: Done - every row and column is mapped.
Click X when no light changed after pressing both buttons.
Haven't placed the sandbags yet? Do the Sandbags helper step first - it gives you the pattern of lights this mapping lets you switch on. Your progress here is saved in your browser.