The Cisternone Romano is an underground water reservoir, in Albano Laziale, near Rome, in Italy.

 I believe there might be a confusion in your statement. The "Cisternone Romano" is not an underground water reservoir but a well-known structure in Albano Laziale, Italy. It is an above-ground monumental cistern, not underground.

The Cisternone Romano, also known as the Roman Cistern, is a large rectangular basin located in the central square of Albano Laziale, a town in the Metropolitan City of Rome. It was built in the 2nd century AD during the Roman Empire and served as a water reservoir for the city. The cistern is made of Roman concrete and has been preserved as a historical and architectural monument.

If you were referring to a different underground water reservoir, please provide additional details, and I'll do my best to assist you.