As you pass around the top of the Grand Lobby, the main corridor extends fore and aft. If you go forward you'll get to the lifts and stairways of Stairway B. If you go aft, you'll pass the Chartroom on the starboard side, and Sir Samuel's on the port side, passing Stairway C and finishing up at the top level of the Britannia Restaurant.
Standing at the top of the Grand Lobby, looking forward
Standing at the top of the Grand Lobby, looking aft