×All secret rooms are accessible from this level. Nine are hidden, while one (3W) is one that you encounter while normally traversing the hold.
Of the other nine, six are directly accessible from a room on the main loop, and the other three require you to travel a bit further afield.
Those three are found at:
Click here to view the secret text
×
2N2W
Click here to view the secret text
×
2N3W
Click here to view the secret text
×
2N3E
If it's not one of those, then keep looking around the loop. I can post a full list if you need.