The Long Day — Robert Harrison

Bishop Avery, a physicist, creates a window to another universe. While he is looking in others are looking out. He and his crew are seized by a force from the other side and taken on an epic adventure in an alternate reality, with characters and beings unlike anything seen before. There are allies and friends, horrible monsters and dark times, but this is mostly a 'feel good' adventure. There are numerous twists and turns with an unexpected and satisfying ending that makes the reader glad they took the journey.