Each level in Journey of Dreams has symbolic meaning:
The first dream takes him to an idyllic village. This represents his desire for a more normal, balanced life with simpler problems. He wants his Dad to be there for all his minor scrapes and scuffles, not to be a problem himself.
The next is an amusement park which he visited with his father every summer except the most recent one. It is active, yet empty and represents his loneliness. One of the most important features is the giant beanstalk- this represents how, ultimately, his self-esteem does not hinge on his father's presence in his life. Ultimately, he understands that his dad simply can't always be there. He's stronger than he knows.
Finally, he visits a world full of fun for all ages, including a giant, colorful playground. It's full of the primary colors - red, green, and bluenote These are the primaries in physics, not art. The playground is bright and cheerful, and it is eternally daytime. The other half is a tall, bright city full of neon lights. Each of the neon lights is either cyan, magenta, or yellow, the secondary colorsnote These are the secondaries in physics, not art. It is always nighttime there. At first glance it seems to simply represent his desire to hurry up and become an adult. But the presence of the playground, as well as the much brighter colors, reveals insecurities and fears about leaving childhood. He meets Helen for the second time in this world and leads her through the "adult" section before exiting the "child" side. It is in leaving the adult side willingly that he comes to understand how mature he isn't. Ironically, in this act, he has begun to grow as a person.
Her first level is a beach. This obviously represents her desire to spend time with her friends and her mother. There is a distinct nautical theme- water is the element of change, but also of healing. It represents her desire for her mom to understand that she's a growing girl who's beginning to have divergent interests. She has yet to fully consider her mom's feelings in all of this.
The next level is made of glass. It's outright stated that this represents her fragility. It is also the dream most linked to her waking life- if you look closely, there's a poster for the Crystal Castle in her bedroom. Despite everything being fragile, nothing breaks. Like the beanstalk in Will's world, this represents her true strength of heart. Here, she comes to understand her mother more.
The final level is a forest that she visited as a child. Like Will's final world, there's a daytime and a nighttime. However, they are intertwined and change according to Helen. This represents how she already feels like an adult, and thinks she can switch between adult freedoms and childhood freedoms at will. When she becomes lost in the woods, however, she tries desperately to be a brave adult to get through it. Though this is a necessary component of her escape, she only fights Nights in the daytime, in childhood. When she does this, she accepts that she is still a child who has responsibilities to her mother- and a need for her. After this, she can no longer go to the "nighttime" forest. The child and adult parts of her are simply one.
The Hub level acts as a gateway to the various components of themselves. It is always nighttime there- just being there makes them feel grown-up. It is a happy yet ominous place. The beautiful plaza masks the interesting rocks and tunnels- but one wrong step, and it's a Fate Worse Than Death.