Geeze, i must be missing something simple, but i can't find the way into nightingale hall; i've "discovered" the location, and in the general vicinity is this large dark longish stone, but i can't for the life of me find the way into the place, even though i can "see" the entrence on the local map; i search and search and seem to be "on top" and all around the keyhole entrance, but can't find the way in... what am i missing??

http://elderscrolls.wikia.com/wiki/Nightingale_Hall

theres a picture of the entrance.

if youre really stuck, fast travel there, it should drop you in the doorway.

yes, i did "fast travel" there, and still no go; but, the link you provided is helpful; in part, the information states: It is only accessible after starting the http://elderscrolls.wikia.com/wiki/Thieves_Guild_%28Skyrim%29 quest http://elderscrolls.wikia.com/wiki/Trinity_Restored_%28Quest%29

So, i guess that's why i can't get in; i haven't started that particular quest yet, so seems like the entrance won't be available until then; guess that's the reason the entrance isn't "there" for me yet.

Exactly.... not sure why you have 2 threads on this. But yeah, you're a LONG way from getting access.