Last Opened
In The GIMP File menu under the ToolBox above the Quit entry, you will find a list of recently opened files. You can click any of these entries to open the file.
 | You can configure how many entries are shown here in the Interface section of the Preferences. Setting this to zero turns the list off altogether. |
 | The list of recently opened files constains the first entries of your Document Index. Look there if you want to see the list off all files you opened since you installed The GIMP. |
Additional Information
Default Keyboard Shortcut: Ctrl-<n> (where <n> opens the <n>-th image in the list of recently opened files).