You can find the Physics Theatre in mid campus. It is very close to the Keith Burrows Theatre. You'll see signs when you get close.
Advice for anyone, if you have a class in the OMB (Old Main Building), get there at least 20 minutes to find your room. The OMB is a maze.
OMB230 means it is room 30 on the second floor. Both the Physics Theatre and the OMB are in the same building on the map.