Belonging to the Agion Anargyron Monastery in Kasteli, it is among the most important churches on Spetses. Built in 1793 by Em. Papatheodoros, it was the cathedral of the island and was the largest church until the temple of the Trion Spetsioton Martyron was built.
Agia Triada is an important Byzantine monument and holds valuable examples of Byzantine paintings from the mid 13th century and earlier Aiginis and Mistra frescoes. The most important frescoes are the Analipsi (Ascension), Gennisi (Christ's Nativity), parts of the Kimisis tis Theotokou (Assumption) and the Pentecost with the "Mother of God One of the Trinity" inscription. Over time, the frescoes suffered significant damage and today none of them have survived intact.