This opening is even tougher. Kill the SS, get the goods and prove your worth. They are coming from both sides.
The Gold Key is behind a pushwall near the entrance.
Eliminate quickly the guards when you get to the gallery of armours. There are SS and officers behind them.
Get ready for more heavy fighting in the southern and central parts.
The Silver Key is in a secret room not far from the entrance but accessed through the central area.

There are two 1-ups in this level, locate them before eventually pushing the wall in the north-western corner. Then get ready for floor 9.