What do the crew see on their voyage that they take for a omen of good luck?

The crew saw a big bird named Albatross and took it as an omen for good luck.

Explanation:

The mariner recalled his voyage across the sea in which he encountered a great storm that nearly swept off his ship and crew members. The storm pushed their ship into a land of mist and snow, a big maze of ice trapped the ship making it unable to move forward. Suddenly a great big sea bird 'Albatross' flew around the ship and then the ice spilt open followed by a sudden wind which propelled the ship out from where it was trapped. The sailors saw this a good omen gotten from the Albatross.