Pushing the wall to the left reveals a gold key door leading to a 1-up. Open the elevator door and enter a strange room. Past the columns you see two 1-ups. Open the door to the right, and get confronted by a skull. This is a secret passage back that you may use later. Get past pushwalls to move on. Now start the desperate battle to get through the green moss-, beige panel- and red/grey brick areas. Know that getting the fallen enemies' ammo may be the only way to get onward. You may get someone to open a silver key door in the south-east leading to the north end of the room with the Silver Key, but still you have to confront a whole bunch of SS behind wooden barrels. If you get stuck beyond the second silver key door a set of secret doors take you back. On your way to the grey stone area find the secret passage to the chaingun and a 1-up. From here on it's still nothing but heavy fighting ahead of you. The Gold Key is found past the north-western room in the brown panel section. The central area includes several secret passages to 1-ups and other goods, but also 5 Grosses. See how many Grosses you can defeat.