From under the Haunted House, go to the merry go round. It's time to disable bombs, so go to the control panel. Open a phonebox next to it.
Attach a phone to it.
Then click on a control panel.
A riddle appears. You have to click on grey balls inside, to light up the exterior ones. Those in the center change color from grey (inactive) to yellow, green, blue and red at the end. They different colors light up different ones at the edge. The rule is, that inside you have to have 4 green, yellow, red and blue balls.
During clicking on balls, the statements about bombs appear. Remember, that changing colors inside you can't light off the previously turned on balls.
One of the solution on the photo above.
You unlock another achievement: "Minesweeper". If you havent' omit any riddle, you get an achievement called "The Brain".