One of Iraklio's most striking ruins, this 13th-century Dominican monastery has been rebuilt and repackaged (mosque, movie theatre) numerous times throughout the centuries. Unusually located right on the sea wall, the monastery contains some beautiful 15th-century frescoes, as well as a modern mosaic exhibition by Loukas Peiniris that is well worth checking out.
Excavations in the surrounding area have uncovered graves dating to the 2nd Byzantine period. Monastery caretakers can be quite pushy for a donation.