Build a solid house of cards with your set of playing cards. Build the walls with pairs of cards with the same value or suit, build the roofs with single cards. Walls need to be supported by walls with the same or a higher value. There are 2 special pairs: 20 and 21. Both can be placed on walls with lower values and a pair with value 21 even increases the strengh of the supporting walls. Complete the house to advance to the next level.