Hellenic Cosmos is a modern cultural centre and museum on the old industrial axis between Athens and Piraeus. Its strength is interpretation: multimedia shows, virtual-reality-style presentations, and exhibitions that make Greek history more approachable for visitors who are not classical specialists.
It is outside the tight ancient-centre circuit, so plan it deliberately rather than expecting to stumble across it. Families and repeat visitors to Athens will get the most from it, especially when the current programme lines up with their interests.