Books in the Sword Art Online Progressive C series

"Asuna and Kirito have made it to Aincrad's sixth floor, where in the town of Stachion they find something very odd--puzzles everywhere they look. New mysteries and complex riddles await, many of which can't be solved with a sword...Fighting against the odds, the two will have to put their heads together if they want to make it out alive. But as they focus their attention on confronting the challenges ahead, will they be ready for the sinister forces that lie in wait?"--Amazon.