The Crystal Marsh is an area in Deliverance.
After becoming a Yalortian, the player gains access to the Crystal Marsh, which must be crossed to reach Aldea, the city of mages. The Marsh itself has very little plot involvement, and exists really just as a barrier. To glitch the game and cross it without beating the Fallen Priest, walk in, walk out, and move up. Repeat to break out and get to Aldea. This leaves you incredibly underpowered, however, so it is not recommended. Unless you only buy tomes there, and go back to where you started, making you overpowered for the area.