Nightingale

While exploring the halls of their hospital ward, three teens with cancer discover a portal that leads them to NIGHTINGALE, a magical world inhabited by a race of sentient machines. The teens embark on an epic adventure to save Nightingale from a malevolent force known only as The Darkness before it can breach the portal and infect our world. Along with the help of their empathetic doctor, whose mysterious connection to Nightingale is more than it appears, the twists and turns of the teen's quest allows each to confront the fear of their diagnosis. Now, not only do they have the chance to escape their pain and be kids again, they can finally feel like more than just victims of their disease. They might even have a chance to be heroes. - IMDb