Locating external references

I'm using Excel 2013. I have a fairly large workbook with multiple worksheets. When I open the workbook, Excel asks if I want to update external links. How can I locate those external references without scrutinizing every cell? Excel Help provides a way if I had Excel Professional Plus 2013, but I don't have that.

Thanks for any help.

This may help you as well http://j-walk.com/ss/excel/usertips/tip054.htm

Thanks to both! I found that one cell in the hinterlands of one of my worksheets.