Here is the full list of all 16 Argol - there are Kronoss' Castle achievements.
Defeat Vampyre Queen
Defeat Thanatos
Defeat the guardian of the castle
Defeat Medusa
Defeat Cerberus
Defeat Phobos
Defeat Deimos
Defeat Kronoss
Release Pegasus
Save Demetria
Kill Kronoss
Release all the prisoners
Find all hearts
Earn more than 100,000 gold
Find all lyres
Find the 12 golden keys