The Nymphaion (sanctuary of the Nymphs) is situated to the west of the city of Nikopolis, near the western gate of the Roman wall. It consists of two buildings serving as reservoirs (cisterns) that provided the city with water. The local residents know the monument under the name of ?Boufi?. Though dated to the time of Emperor Augustus, recent investigations in the area date the edifices to a much posterior period, i.e. in the second half and the early third century AD.

The Nymphaion is constituted of two opposite buildings that are 23m apart. Their fa?ade is simple and unadorned, they are made of bricks and they both have niches on the interior. They do not stand on the same axis, which attests that they were not erected in the same construction phase. The reason for their construction is to shelter the two large water reservoirs that were filled with water coming through an aqueduct from the sources of Louros River, in Nikopolis. The external walls of the buildings were not decorated, whereas the interior (each wall about 17m in length) features alternating rectangular and semicircular niches. The niches situated 1.85m above the reservoir, were incrusted with marble. They were ornate with marble statues relating to water and nature, while the wall under the niches had a limestone revetment. Low parapets shut off both sides of the edifices that were open. Consequently, the statues were visible for those who came by the western gate. The water that overflowed out of the reservoirs was channelled into earthen aqueducts, probably placed at the fa?ades of the buildings.