Noah's Ark

In 2100, mankind is facing the threat of environmental destruction and population explosion. Because of these threats, mankind is proceeding with the terraforming of Mars in preparation for migration. However, just before the plant base is completed, a huge tower suddenly appears from the ground. Investigation reveals that it was built about 5 billion years ago and has seven floors inside. An investigation team (the player) was sent to infiltrate the tower and to discover the mystery on why and who left this tower behind and for what purpose.