There are two floors that allow access to the Princess Theatre and 4 entrances. I point this out because many people complain about walking through the casino / smoking area BUT it can be avoided.
The casino floor has one entrance on the non-smoking side of the casino and one entrance on the smoking side. The upper floor has two sides as well but leads to the upper section of the theatre.
The entrances are usually on Deck 6 and 7 on most ships. On some ships, there are 2 additional entrances on the far sides with stairs leading to entrance.