Footprints

The Warriors spot some footprints on the dusty stone floor that lead to a blank section of wall and vanish.
If the Warriors investigate, roll 1D6 on the following table:
1 Roll 1D6 for each Warrior. The Warrior with the lowest score is hit in the head by a spiked metal ball that swings down from a concealed hole in the roof. He suffers 2D6 Wounds, with no modifier for armour except a helmet. If more than one Warrior rolls the same lowest score, these Warriors are all hit.
2 The Warriors find nothing.
3-6 The Warriors find a concealed door. Place a doorway on one of the two blank walls. Take 1D6 extra Dungeon cards that have been put back in the box, making sure that none of them are objective rooms, shuffle them, and put them in a pile face down by the new doorway. Randomly take one of the spare objective room cards and place it at the bottom of the new deck. If the Warriors explore this sub-dungeon, roll twice on the Objective Room Monster Table to determine what the extra objective room contains.
If the Warriors kill all the Monsters in this extra objective room, each of them gains 1,000 gold!