The Hero's Journey is a framework that scholar Joseph Campbell came up with that many myths and stories follow. Many storytellers and story-readers find it a useful way to look at tale. (That's actually putting it lightly. Some people are straight-up obsessed.) Chris Vogler adapted Campbell's 17 stages of a hero's journey, which many screenwriters use while making movies. Vogler condensed Campbell's 17 stages down to 12, which is what we're using. To read a general explanation of the 12 stages, click here.
Thor's story doesn't fit perfectly into the Hero's Journey structure, but we're giving it a shot. As the gross old saying goes, there's more than one way to skin a cat. Here's how we've diced up the story:
We don't get a great sense of the "ordinary world" in this story – Thor wakes up one morning to find his precious hammer missing.
According to the Hero's Journey structure, a character's quest begins with some sort of call to adventure, after which the hero realizes that everything is going to change. That's definitely the case for Thor in this story. He finds out that not only is he going to have to venture into Jotunheim without his hammer, but he's going to have to pretend to be a woman.
As you might expect, Thor is totally resistant to this scheme at first, afraid that the other gods will laugh at him once he's all decked out in girly clothes. He therefore engages in a "refusal of the call."
Luckily, Thor's gets some help from Loki (who you wouldn't normally think of as a mentor). Loki convinces Thor to don a bridal gown, and also offers to tag along with him as a bridesmaid.
Thor puts on a dress and veil and allows the other gods to deck him out with jangly keys, jewelry, Freyja's precious Brisingamen necklace, and a pretty hat to cover his head. A woman's world is definitely an unknown and scary realm for Thor. As Thor and Loki cross over into Jotunheim and head toward the wedding feast, Thor enters the "crosses the threshold." Things are about to get serious.
Now Thor's "tests" begin as he and his ally Loki infiltrate the land of the giants. First, Thrym notices that his "bride" has a rather large appetite. This observation threatens to blow Thor's cover, but, luckily, the quick-thinking Loki comes up with an explanation involving pre-wedding jitters and fasting to overcome this first test. Next, a glance beneath Thor's veil reveals his scary, fiery, un-feminine eyes, but again, Loki manages to explain this away as the sleeplessness of a nervous bride.
Thor doesn't seem to suffer any of the doubts that many heroes feel during Stage 7, nor is there any one "ordeal" that particularly stands out.
Once Thor's hammer is placed in his lap, he achieves "the ultimate boon." He achieves the goal of his quest, which is to get his hammer back. Since it's Thor we're talking about here, he kills a lot of giants in the process.
"The Theft of Thor's Hammer" concludes before Thor and Loki return to Asgard, so we don't really see a "road back."
Once Thor starts slaughtering giants, he's no longer at all concerned with pretending to be a woman, so it's like his old, masculine self is brought back from the dead. The Thor we know is probably more than happy to be a manly man again, and probably doesn't at all mind saying good-bye to his feminine side.
Though we don't see Thor return to Asgard, we know he heads home with his hammer. The hammer is an "elixir" to the gods of Asgard, because it's the magical tool that allows Thor to protect them from the threat of giants.