Through Abandoned: The Underground City is the first part of a big story about parallel worlds. Those worlds are very strange, because people left them forever. You should explore those worlds and find your brother who dedicated his life to find a way into Abandoned and disappeared there.
Through Abandoned: The Underground City is a classical point and click adventure. Solve puzzles and play mini-games, look for items and find a way to use them, explore, enjoy the story and try to escape.