The entrance to the stash itself is behind the crown picture. To get up there you'll need the gauss and a bit of skill. There's a crossbow in the stash.
But if you turn around to face the wall, you'll bump into a door. It opens when you press "E". The door opens and you see a passage leading down.
Once a player jumps down there, he starts taking damage, and if you don't figure things out quickly, you can easily die. There's another passage in the floor. It leads to a gravity room, which can also be found on the crossfire_emperors and levels maps
Gravity gets lower if the player walks into the right doorway; walking into the left one brings gravity back to normal. The gravity only affects the player who has walked into the doorway.
One more little secret is the green crown. If a player sits on it, his health will be restored. From the top it refills slowly, but if you rub up against it from the side, your health will refill much faster. And if you gauss jump and slam into the bottom of the crown, the player's health goes up to the maximum.
