I see that an article "the" is needed to describe the headquarters of the US Department of Defence: The Pentagon.
From my grammar book to show the usage of articles, I found that "the" is not necessary with companies, e.g., Microsoft, nor with major landmarks, e.g., "Central Park". However, "the" is necessary with building names, "the Hilton".
So, "the Pentagon" uses an article "the" to symbolize the building? In general, is there any good logic behind the usage of "the" with proper nouns?