While in the sewers a little jumping on the floating logs will
reveal a four-leaf clover (a life).
If you keep going around the circle on the logs you will also
come to a box and a key under the walkway.
The key opens the door in the sewer wall.
Now every time you go in the room and then come out, two things happen. The box and key reset themselves in the sewer, and the four-leaf clover resets. Use this to fill all your clover boxes.