One or more Death Knights attacks you from a parapet. To get up there, go to the far-right corner of the corridor with the flashing lights. There is a square hole in the floor, jump down. There is goodies and a slipgate, that will send you to the parapet.

Carry on left around the room on the narrow ledge to get a reload of rockets.

Dive into the moat in this or the next room. At the far wall of the next room is a submerged entrance to a goodie room.

Before you dive into the funnel, shoot the "Q" on the roof beam. Never mind the missing roof. A secret door opens.

Before you exit, shoot the recessed floor tile. A goodie room is underneath.