Here is the list of secret achievements you can unlock for an additional 100 gamer points in The First Templar on the Xbox 360.
A Lady with an Attitude (10) – Rescued Marie d’Ibelin
An Honourable Enemy (15) – Defeated Muzafar
Beast-Slayer (10) – Defeated the Beast
Friday the 13th (15) – Survived the events of Friday the 13th
Saviour of Acre (10) – Survived the siege of Acre
The Cup of Christ (15) – Found the Grail
The Hero of Cyprus (10) – Rescued the messenger of King Philip
The Lost Temple (15) – Explored the Temple of the Nine