The Swamp of Infinite Sorrows was the first location that appeared on the Map to the Wishing Star and in the Dark Forest when Kitty Softpaws first touched the map. Just like the Valley of Incineration, the Swamp of Infinite Sorrows has steppingstones, but the stream and the trees are completely different. Under the grayish sky, this stream is made from green glowing goo with fumes rising out of the hollowed stumps.
It was meant to symbolize her intense emotional trauma and wallowing from her heartbreak whenever she "let her guard down."