Opus maintains two separate lists of recently visited folders.
The recent list is a global list of your most recently visited folders. It is displayed in the Recent Locations sub-menu in the drop-down menu shown when you right-click the the Back button on the Location Bar toolbar.
It is also displayed in the drop-down list attached to the breadcrumbs path field.
It can also be shown in the folder tree - turn on the Recent List item on the Folder Tree / Contents Preferences page.
You can configure the recent list from the Recent List page in Preferences.
The history list is also a list of the most recently visited folders, but it is maintained on a per-file display (or per-tab) basis. The history list forms the basis of the back and forward navigation actions - when you click the back button, you are moving back through the history list.
Right-click or click-and-hold the Back and Forward buttons on the Location Bar toolbar to access these lists as drop-down menus.
You can configure the size of the history list (the maximum number of folders remembered) from the Recent List page in Preferences.