The Cave of Lost Souls is a cave that was formed in the Dark Forest. It emerges after Puss in Boots touched the Wishing Star map in an attempt to help Kitty save Perrito… again. On the map, this cave is near the Wishing Star.
The cave allows Puss to encounter reflections of his previous eight lives in crystal and confront the poor life choices he made in the past. Each of Puss' former lives displays the same negative qualities that led to the deaths they represented. Puss initially dances and sings "Fearless Hero" with his lives.
When they turn on Puss, critical of his friendship with Perrito and his cowardice, Puss becomes disgusted with himself, seeing his own arrogance turned back on him.
Death then appears in the cave (despite there being no visible entrance), reinforcing the arrogance of his lives and threatening to take his "last life." He proceeds to shatter each crystal, horrifying Puss into running away. The crystals begin to take on a red tint when Death was chasing the cat. This causes Puss to run for dear life toward the star, abandoning Kitty and Perrito.