You have to be either an Account Owner or a Workspace manager to be able to archive Workspaces in your account.
1. How to Archive a Workspace?
You can archive a Workspace along with all of its belonging boards. To do that, click on the "Workspace Settings" icon of the corresponding Workspace and select “Archive Workspace.”
A new window will appear with information about the Workspace and the Boards you want to archive (see image below). If there are any unfinished cards on any of the respective boards, you will see their number in the “Unfinished Cards” column. You can click on any board name to open it in a separate window and review the unfinished cards.
Important: If you archive a Workspace, all Boards in that workspace will be archived irrespective of whether you are assigned to them or not. To see which boards you are assigned or not assigned to, click on the filter icon in the Filter field. Once ready, click on the "Archive" button to archive the workspace.
All archived Workspaces in your account are stored in the "Archived Workspaces and Boards" panel of your account and you can access and restore them anytime.
2. How to Unarchive a Workspace?
Go to the Home Dashboard of your account and select the “Archived Workspaces and Boards” button.
To restore the archived Workspace, you need to unarchive at least one of the boards that belong to it.
You can restore all or any of the archived boards. The restored Workspace will become available on your Dashboard.
Note: You can permanently delete a board from the same panel.