Each player in turn must take one of their columns from any level except the highest, and place it on the highest floor. If they cannot remove one of their columns, they may ask to place the next floor. Each opponent may challenge this decision; if they choose to do so and are successful, they may remove that piece from play, and the player misses their go. If no opponent challenges the player, they may place the next floor on top of the pillars of the current highest floor - again, it must lie completely above the base mat and cannot partially cover any column.