I'm dying here, because I have a very complete plan of these rooms, but no way to post it! However, to add a few more details: From the Concert Hall, you enter the Malachite Hall; that opens to the Arabian Hall (long, narrow, extending south toward Palace Square); that opens to the Rotunda, which in turn leads to the Dark Corridor; directly off the Rotunda, opening east, was the private chapel. From the Malachite Hall, doors opened to the White Dining Room, facing a small inner court. Also from the Malachite Hall, doors opened to the Empire Drawing Room, overlooking the Neva, then came the Silver Drawing Room, then Alexandra's corner Drawing Room. Continuing along the side of the Palace was the bedroom; then A's boudoir; door at the back opened to her bathroom which overlooked the small inner court; then A's dressing room. Nicholas's study was at the corner of the wing, connecting two rooms, one long, one short, via an arch. His bathroom was reached from a door on the right side of the bed-down a corridor-it overlooked the inner court. From N's study, a passage room, then a room for an adjutant, these extending back on a west-east axis, into the body of the palace. His Library opened off these, then next his Billiard Room, then his reception room, next to the Saltykov Stair.
As to his bath and tub-I've got copies of the plans for the room. At the WP, Krasovsky designed a tub, set in a recess lined with concrete and faced with Dresden tiles, which was reached by eight marble steps; it was indeed sunken.