The Can'-Ka No Rey ("The Red Fields of None") is the field of roses surrounding the Dark Tower. The roses are very difficult to remove from the ground. They have thorns that can rip into hands while they are in the ground, but become harmless after being removed. The roses call people to come to the Dark Tower. Their call is strongest at sunset.
The roses are dusky pink on the outside, fierce red on the inside and have a center as yellow as the sun. One of the roses was said to have been taken to Our Lady Of The Rose and an entire garden grew from the single bloom.
The field is the scene of the final battle between Roland Deschain and the Crimson King. The King is locked outside the tower on a balcony and can only throw sneetches at Roland while waiting for him to be drawn to the Tower (because at sunset, the Crimson King knows Roland won't be able to resist call of the roses). Roland's secret weapon is the artist, Patrick Danville. Danville draws a picture of the King and uses a combination of dye from rose petals and Roland's blood to color the Crimson King's eyes. After
the picture is complete, Danville erases everything except the eyes.
It is worth noting that The Tower is surrounded by roses, much like The Rose (twinner of The Tower) is surrounded by towers (in New York).