Celtica, a Myst clone released by H+a Entertainment in 1998.
From the CD case: "In a lost and barbaric age, an alien race travels to earth and leaves behind the secrets of Celtica! What mysteries lie in the Ascension Amulet? What secrets are contained in the Book of Ascension? Who has been deemed worthy enough to unlock these riddles and ascend to the domain of this forgotten alien race? Your time has come, and now, on this mysterious island, you must confront the ageless secrets of Celtica, and seek out the doorway into a world beyond time, into a world beyond the boundaries of reason."
