Of all his many adventures, can you establish an "inmost cave" experience for Theseus? What does he learn from it?

In terms of the hero's journey, as theorized by Joseph Campbell, the inmost cave refers to that most dangerous place in the other realm, the realm outside the hero's comfort zone, which he must enter if he's to achieve his ultimate goal. In the case of Theseus, his inmost cave happens to be a literal one, the cave of the Minotaur. Before he reaches this stage, however, he must encounter many dangerous challenges on the approach to the inmost cave. On his way to his epic showdown with the Minotaur, Theseus must do battle with, among others, Club-Man, Periphetes, and Procrustes.
But the biggest challenge of all lies in the inmost cave itself, the cave of the Minotaur. Theseus has vowed to slay this savage beast—half-man, half-bull—not just for his own glory, but for the good of Athens. If he prevails against the monster, then he will be a hero; if not, his name will live in infamy, and the Minotaur will continue to snack on Athenian children.
In slaying the Minotaur, Theseus must overcome his deepest fears; he must enter the inmost cave to achieve his ultimate objective. Thanks to his deep reserves of courage, not to mention a little help from Ariadne and a ball of string, Theseus is able to exit the inmost cave, grateful Athenian children in tow, having successfully accomplished this most perilous of missions.