The castle consists of a strong square tower and an enclosure fielding six cannon. The two different kinds of masonry visible today represent two construction phases: the first at its foundation in 1205-1210 and the second probably at the time of the second Venetian occupation (1687-1715).
The tower is almost square in its ground plan, with an entrance on the south side. The interior was originally one, but later on it was divided into two areas by a wall, built of the same, block-like grey limestone as is the precinct-wall of the fortress. This dividing wall runs north-south and has an arched door connecting the two spaces.
The enclosure has on its upper surface six cannon-embrasures oriented in all directions around the hill. Inside the enclosure, and abutting the south side of the tower, is a cistern that belongs to the same building phase as the precinct, as do the ruins of a small rectangular building. The tower and the enclosure have different types of masonry.
The tower is built of limestone rubble of a medium-size with pieces of tiles positioned between them in a haphazard arrangement, so as to surround each stones (cloisonné). An exception is its eastern wall, of which only a portion in the central and lower part is made from this early style of masonry. The remaining part of the wall seems to have collapsed, and was reconstructed with well-worked rectangular limestone blocks, with much less use of tiles between them. This second type of masonry is late in date: the precinct of the fortress is so constructed.
The first masonry tower in Penteskoufi has similarities with the north-east outwork of Acrocorinth, and is roughly analogous to most Frankish castles in the Peloponnese, with the exception of Chlemoutsi and Glarentza. The later stonework in the tower resembles the late masonry of the Frankish tower on Acrocorinth.