Once you reach the town area, you need to activate a torch just to the right of the bird nest. Walk past the statue and go up the slope. At the top, climb on top of the building's roof and up again to a control panel. This controls the torch in the middle of the two buildings.
On the left panel, press the down arrow once to turn it upside down. Move to the right panel and click on the left button once to turn on the water and flames. The torch will be lit. Press the up arrow twice to take the torch back to the top (while still upside down). Move to the right panel again and click on the left button twice to turn the air back on. Click on the up arrow again to turn the torch the right way up. A new button will open up on the right panel -- click this button to lock the right shield into place.
to back away from the control panel. Jump from the top of the roof onto the lit torch. Teku will set himself on fire and you'll get the achievement.