Interregnum is a solitaire card game using two decks of 52 cards each. The object of this game is to build eight foundations of thirteen cards each, regardless of suit. Building the foundations is unusual compared to most foundation-building games.
The game starts with eight cards dealt in a row. The space below each card is a foundation and the card above the foundation is its last card. Therefore, the foundation must start with a card which is a rank higher than the card over it and is built up from there without any regard to the suits. (E. g. a 5 above a 4, a 2 above an A, an A above a K, etc.)
Below the foundations are eight tableau piles each starting with one card each. The cards on the tableau must be moved to the foundations and there should be no further manipulation within the tableau. When no more moves are possible, a card is dealt from the 88-card reserve (the leftover cards) into each pile, whether empty or having at least one card. The top card of each pile is available for play.
When a foundation has been filled to the twelfth card, the card above the foundation is placed over it as the thirteenth card, closing out the foundation and setting it aside.
The game is over when the reserve has been used up and there no possible moves left. The game is won when all eight foundations have been set aside, each with thirteen cards each.
Sometimes, the first eight cards dealt (as mentioned above) are the foundations and are built the same way as if they are the first cards. Once a foundation is filled with thirteen cards, ending with the card a rank lower than the first card, it is closed out and set aside.