The phrase "dark corners" refers to hidden or secret places that are not easily seen or known about. It can also represent unknown or secretive aspects of a situation or person. Full definition
Light candles everywhere, and add a few cosy lamps in dark corners of your house. (creativeboom.com)
This is an important decision and running a tenant background check will shine lights into dark corners to help you make the right call. (rentprep.com)