It's pretty hard to get lost in the main part of the library--it's really just a big rectangle.
Lewis Annex is a different matter and can be confusing. Remember to use the elevator to navigate between the different floors and that you need to be on the fourth floor of Lewis Annex to get back to the main part of Pius Library.
You can always call the Information Desk at 314-977-3087 for help. If it's between 9am and 5pm Monday-Friday our on-call librarian can come meet you and help you navigate your way to the book you need, or even just help you get out of the Lewis Annex!