When you have collected all 12 Secrets in the regular four Golden Mask Levels, you can enter the Secret Bonus Level "Nightmare in Vegas". To do so press new game after finishing the game with 12 Secrets. Then pick "Nightmare in Vegas" from the menu.
Lara's Room

Lara starts this level in a bathroom. There's nothing to collect. Press the
button to open the door. In the bedroom press the
switch on the left to open a little storage-room. Collect a
large and a
small medipack, two packs of
shotgun ammo and a pack of
flares there. Then open the door to the balcony. If you look out to the left you can see two killers in the next room. Get back into the bedroom. Collect the
shotgun and the
ammo on the window sill. Then push the
button under the TV.
(This will show you the trapped butler in the bathroom of the killers' room.) Now run towards the main door. It will open if approached. Get into the corridor.
Balconies

Run to the left. At the end are two closed doors. For one you will need a key. So instead climb onto the window sill and shoot the window. Go outside. Turn right and jump towards the gap there. Shimmy to the left. At the end place your feet on the ladder and climb down. Climb over to the left and then up. Through the window you can see the baddies. This window is bullet proof.
Baddies' Hotel Room
Jump over to the balcony on the left. Shoot the windows and kill the two
gangsters. One will leave a
small medipack, the other one will lose some
shotgun ammo. Step into their room and collect the
shotgun ammo around. Press the
button on the left wall to open the bathroom door. Step inside. On the cupboard on the left is another
small medipack. In the shower you will find a
Hotel Key. Pick it up and leave the bathroom. Run towards the hotel room door and run out into the hall.
The Bird Cage

On the left you can find a lock. Use the key on it. Step through the open door and follow the passage. You will come to the hotel's atrium. In the middle is a huge golden statue. Run over to the left. Here you will find a cage and inside another one of those huge bird creatures. Run towards the left side of the cage. On the left column you can find some
flares. Further along on the left side you can find
shotgun shells. This will attract another
baddy. Kill him. And this bastard doesn't have anything for you. Now run to the other side of the cage. On the wall with the entrance you can find another column on which you can climb and from where you can get higher up. Jump onto the nearest walkway and make your way onto the cage roof. There you can find 2 packs of
shotgun shells and a
small medipack. Climb back down and return to the atrium.
Atrium and Statue
When you explore the area you will find that the lift on the left will need a chip to work.

Through the windows on the side opposite the bird cage you can see red carpet walkways and ramps, but you cannot get there from here.
Since there is not much to do, return to the side with the entrance. If you look towards the statue you can see a large medipack. Take a running jump to get there and while in the air press action. You might fear that you won't make the jump but try it anyway. Surprise, Lara will hold on to the sculpture. Climb up and collect the
large medipack.
Take a running jump back. Since you are higher up that's no problem at all.
Uzis and Key in the Pool

Now run back towards the entrance of the birdcage area. Stand on the white square in front of the entrance. When you look down you can see a golden slope and a black square.
I have marked this red in the picture. While standing on the edge of the white tile, make a swandive down and you will land exactly where the black spot is. A trapdoor will open and you will drop into water. Collect the
Uzis and four packs of
ammo. Swim through the passage to get to a door that will open when approached. You will end up in a pool. Collect the
Hotel Key and swim up to the left. Climb out of the water and kill the
guy shooting at you. By the door you will need another chip. Run out into the atrium. You are now on ground level. Run around the statue till you meet two
baddies. Kill them. One loses a
large medipack, the other loses
shotgun shells.
The Jungle - just goodies, can be skipped

Use the key you've collected at the jungle entrance. There is a sign "Three Kings Convention" with dinosaurs on it. Step through the door. Run into the left passage. By the enclosure with the T-Rex you will meet a
baddy. Kill him and gain a
small medipack. Further along you will find a pack of
shotgun shells. Return to the entrance hall and this time run into the right passage. Kill the
baddy on the other side of the cage. Collect the
shotgun shells. Then run back out into the atrium.
Cell Block Rock

Now enter the night club with the sign Cell Block Rock. Inside you will find a couple of tables and chairs and a piano. On the left you will find a
small medipack. Pick it up. On the right is a pack of
flares. Run back up the stairs. On both sides you can see a switch at the wall. Use them both to open the curtains. Kill the four
brawlers coming down from the stage and the guy with the gun coming from outside. He loses a
small medipack and
Uzi Ammo. One of the brawlers was carrying
shotgun shells.
Run towards the stage. Pick up the
shotgun shells. This will trigger two more
brawlers. Look at the swinging crates. There are two higher up than the others. Use the blocks to climb all the way up. If you stay close to the backside of the stage you cannot get hurt by the swinging crate. Take a standing jump onto the block with two packs of
shotgun shells. Climb back down.
Secret 1:
At the back of the stage you will find a closed grate and left and right of it are two movable blocks. Pull them out to fill the gap in the middle row of crates. The trapdoor at the back opens. Drop down. See picture. The green squares are higher up. Blue squares are movable crates. Find the crate in the left corner - the one in the upper right on the pic - and push and pull it into the other corner. Now push and pull the other crate onto that spot. Underneath you will find Uzi Ammo. Then push and pull the next crate against the previous. Here you will find the secret, the Gold Coins. Climb back up and out of the secret chamber.
It's time to leave the bar. Run back out into the atrium.
Elevator
Turn left and find the open elevator door. Step inside and press the switch to call it down. Press the
switch again and quickly enter the lift. Up on top get out of the lift. Drop down onto the ledge before the window. Make a standing jump onto the golden statue part to your right. From there walk through the broken glass. Collect the
Uzi Ammo here. Then take a standing jump onto the starry walkway. Here collect the
large medipack and the
Door Circuit. Take a running jump back onto the golden ledge.
Goodies:
Make your way back to the elevator. If you slide down use it to get up again. Send the elevator down. Jump onto it's roof and climb up the ladder. Get into the passage and turn right. Get down and jump over the broken glass. Kill the brawler on the other side and climb up into the chamber. Collect the Shotgun Ammo. Look out of the window. Slide down the slope and jump to reach the statue. Slide down to the ground.
Outside

Now run towards the pool again. On the other side use the door circuit to open the door. Load your Uzis and step outside. You will be attacked by a
T-Rex, shoot him and if necessary retreat towards the pool. When he is finished, step outside and collect the
flares on the left. Then run between the buildings ahead and climb onto the block. Run into the passage on the left and collect all the
automatic ammo and the
automatic pistols. Step out on the other side. Turn left and kill the
brawler appearing. Run down the street to the right. By the van turn right and find the
Elevator Junction in the little depression. Quickly run into the television shop with the sign "Bartoli" Another
T-Rex will appear, kill him from the doorframe. Then collect the
large medipack and the
flares inside. Get back out. Outside another
brawler will appear. Kill him.
Secret 2:
Then run down the street and into the dinosaur enclosure. On the ground you will find the Gold Bars. Get back outside.
Now return to the hotel.
Sculpture Climbing

Now you have the elevator junction for the elevator up on top so it's time to get back up. Run towards the golden sculpture. Go towards the side with the jungle entrance. Here climb up on the sculpture. Climb over to the left and further up. You can finally pull up onto a platform with
Uzi Ammo. Collect it. Look at the slope to your right. Jump onto it and grab the ledge while sliding down. Shimmy over to the right. Climb further up and on top climb left till you can pull up and end up on top of the statue.
Elevator to Hell
Take a running jump back onto the walkway.
Goodies:
On your left is now an open door, where the red carpet is. Run down the ramp and collect the Uzi Ammo in the first alcove. Kill the brawler. Run further down and collect the automatic ammo in the last alcove. If you step onto the right of the grey platforms outside you will trigger another brawler you have to kill. Run back up to the top.
Now run towards the elevator and use the elevator junction. Call down the elevator by using the
switch. Use the
switch again and step into the lift. On the other side step out.
Goodies:
But do not leave the alcove, or the bird will appear. Instead send the elevator down again. Jump onto it's roof and climb up the ladder. At the top, leave it with a backflip. Collect the shotgun shells and the large medipack. Run up to the top and climb down the ladder into the shaft. You are above the passage with the green floor. The bird is patrolling below. Drop down.
Secret 3:
Instead of fighting the bird monster run down the passage. You can flee much quicker if you jump while running, you also need to jump over the splinters. Run down into the bird monsters cage and pick up the Golden Skull. Now run back up the passage running and jumping all the time.
Goodies:
If you run to the top you will come to an outdoor area. If you are quick enough you can collect two packs of Uzi Ammo and a large medipack.
Fight the
bird with all you got to finish the game.