The Yther Chronicles

Here There Be Dragons! An impossible dream comes true when
Yther's monarch Coleus shows up on Earth, seeking the help of
Abby and her friends once again. It turns out an evil goddess
calling herself the Nightmare Queen has cast a spell of eternal
sleep on all the people of Yther, and there is only one way to
reverse it. Led by Coleus and guided by a mysterious immortal
hiker named Olf, the three human teenagers are taken to a
bizarre cluster of worlds known as the Dragon Zones. Here,
they must battle twenty ferocious dragons in twenty wondrous
and amazing realms, on their quest to retrieve to power of the
legendary Cosmic Core and use it to save Yther.