The fortress of Tholi is built on a spot with panoramic views, opposite the settlement of Alagni, although administratively it belongs to the nearby Meleses. It is an elaborate structure of the late Venetian rule of Crete (16th or early 17th century). Its last use was by the Turks, who turned it into a tower (Kule) to  overlook the entire surrounding area.

Although it looks like a fortress, the experts who studied it state that its construction does not have the characteristics of a fortress. It is more similar to the Venetian Villas Trevisan in Kissamos and Ethia in Sitia. It is thus possible that it was a Venetian mansion built on a prominent position. The structure consists of three vaulted ground-floor buildings with an enclosure, while the original building was two-storey. In fact, the central rectangular building, which remained in good condition until the earthquake of. September 27, 2021, has vaulted elongated ceilings, hence the name Tholi (tholos in Greek stands for vault).

Behind the castle, nearby, there is the two-aisled church of the Holy Apostles which dates back to somewhere between the 15th and 16th centuries. Two impressive arcosolia (burial monuments) can be found here, one next to the entrance of the church bearing the date 1614, and the other inside the church, where the coat of arms of the Venetian Kornari family dominates. Holy Apostles church which was damaged by the earthquake of 2021, belongs to the Sinai Monastery and is today abandoned.