Nearly anything on a Trip can be archived, even the Trip itself!
Archiving not only removes that item from your default view, but also makes it inaccessible to your customers.
When you archive a Trip, all items on that Trip also become archived. The Itineraries, Proposals, Forms, and Decisions all become inaccessible to the customer by archiving that Trip.
How do I archive an itinerary/proposal?
How do I archive a Trip?
How do I find things that have been archived?
To find a Trip that you archived, you can apply the Archived filter. All filters appear at the top of your home page.
Just click on Archived Status, and then check the box marked Archived, and uncheck the box marked Not Archived.
To find a Proposal, Itinerary, Form, or other item that has been archived on a Trip, just go to that Trip and then click on Show Archived: