When using the Finder in OS X, sometimes you may want to have multiple views of the same folder open at once. Usually it's quick to create a new Finder window and navigate to the folder; however, this may be inconvenient if the folder is buried deep in the filesystem, such as may be the case when troubleshooting a problem or two with the system, retrieving a backed-up file, or organizing an extensive tree of work files.
If you need a faster approach, there are several, some of which use the Finder and its capabilities, and others that involve secondary programs.
Firstly, in Finder, you can quickly create a duplicate folder view by pressing Command-up arrow to reveal the folder highlighted in its parent directory, and then pressing Control-Command-O to open the folder in a new window. You can then switch to the prior window and double-click or press Command-O to open the folder directly.
This is convenient for a single duplicate instance, but if you would like more than one duplicate, select an item in the folder and get information on it. Then expand the General section of the information window and note the "Where" listing that shows the full path to it. Select the entire path, starting with the first forward-slash and including all lines to the last folder. Then press Command-C to copy it.
With the path copied, press Command-N to create a new Finder window, and Shift-Command-G to bring up the "Go to Folder" field. Paste the copied path into this field, and press Enter to have the window go to that location. Repeat, creating a new window and pasting the path for any additional windows you would like.
An alternative approach is to make use of the Finder's sidebar and toolbar, by dragging the current folder to these locations to make a link (you can drag the folder from the window title to the sidebar, for example). Then create a new Finder window by pressing Command-N, and click the new Favorite link to set the location. When finished, you can drag the link out of the Favorites.
Similar to the Finder's favorites menu, you can use the Dock by dragging the folder to it (in the user files section between the Trash and the separator bar), and then holding the Command key while clicking the folder. This will create a new Finder window at that folder for each click.
A final alternative is to use Spotlight, provided the folder is in your home directory, on an indexed external drive, or in another area meant for access by your user account. To do this simply search for the folder name and it should show up as a search result. Then select it and press Command-Return to open a new folder revealing the item. You can then repeat this to open additional folders revealing the item.