The Freemarch Puzzle is not actually in Freemarch, but is in the “Lake of Solace”. If you look at your map, the puzzle is directly beneath the L of “Lake”. Swim out to it and make sure you have full breath before attempting the puzzle. Swim directly down to the floor. Here you will find aqua lamps that will for a moment be visible and the next invisible. All you have to do for this puzzle is right click on ever aqua lamp before your breath runs out.
Be in the center of the circle in order to have the best chance of completing this puzzle before you die. When a lamp appears, click on it, and get ready for the next. Once all of the lamps are activated, simply loot the chest that appears and swim back to the surface.