Double Solitaire Turn 3 is played with two 52-card decks of standard playing cards. The goal, the rules, and the scoring are all the same as for Solitaire Turn 3. The number of columns in the Tableau is expanded to 9, the number of building locations in the Foundation is expanded to 8, and there are more cards in the Stock.
The strategy varies a lot from the one-deck version. With so many Kings to place, it's a bit of a balancing act trying to decide when to turn a hidden card in the column with the fewest hidden cards in order to empty a column to place a King, and when to turn it in the column with the most hidden cards in order to maximize the number of cards turned.
With more suits in play there are more ways to build a suit. Most claim that the game is easier to beat than the one-deck version.
For more information, please refer to Solitaire Turn 3