The Passive is used when the action is more important than the person who does it.
To mention the person or thing who does the action we use the word by.
To form the Passive we use the auxiliary verb be+ the Past Participle
The lcehotel is made of ice and snow.
This five-star resort is being built below the sea.
Two people were murdered while the castle was being built.
It has been fully restored.
It will be Linked to land through two tunnels.