Blackwater Park
Note: While it is possible to get through this area without using a costume, it is very hard to reproduce. I will leave a discription at the end for those who are interested but be warned that it will take possibly dozens of tries to get the timing just right.
Move to the fields to the right of the hotel and take cover behind some potted plants. Slide left until you've entered the restricted area. Keep sliding right past the planters. Keep going until you come to the outer wall of the park. Move along the wall, keeping it to the right. When you find the parking area, grab the gas can and then take cover behind the black car. Wait for the plumber to come closer so he is the closest to you (you may have to move up for this) and then toss the gas can in between the van and the black car. You can now subdue him without anyone seeing.
Take his outfit and dump him in the laundry basket just to your right. Now that you have his outfit, follow the road as it leads down to the garage. Just before the garage doors will be a security room and inside will be Evidence. Come back up and get onto the grass on the right. Walk into the janitorial area here and then move through the building to the back. In the office room at the back will be a vent that you can climb into. Climb into the vent.
Exit the vent, go through the room and then up the stairs to the left. At the top, use the checkpoint and go into the next room. Immediately turn left and enter the office with the long row of windows. Sneak around the desk and use the computer when the coast is clear. Make your way over to the elevator and activate it. Vacate the area until it arrives and then get on.
The Penthouse
Your Plumber disguise will be useless from here on out so be careful. When you disembark from the elevator, move left along the ledge and then drop down to the catwalk. Walk through the doorway and turn right. Go through the wooden door to enter the lobby. Make a hard right and go up the giant staircase. Take a right to go up more stairs and at the top, hug the right wall to go through a small hallway.
At the next intersection, you should see a couple of guards guarding a door to the left. You need to get into that door. Wait for them to leave or make a distraction to get by them. Inside the bedroom, grab the keycard from the night stand. Now undo everything and return to the elevator. Drop down into the elevator and immediately take cover.
There will be two guards in the room beyond. You'll need something to throw. Throw it over their heads and then while they are turned away, slip into the room and immediately go right to find the door with the keycard reader. Go through the door, down the hallway and investigate the wall next to the large globe on the left. There is a door here so open it and wait just inside by this doorway for Layla to come in. Kill her and be sure to pick up her unique weapon.
Dump her body in the crate in the corner of the room. Pick up the phone on the bed to end the mission.
Blackwater Park - Suit Only, Infiltrator
Make your way to the far right without getting the plumber costume. Get over to near the janitors supply house. You'll see a street leading into the garage and the supply house on the right. Before that, you will see a water pump. Grab the gas can near the pump and then shut off the pump.
Go around the left side of the pump, past the pillar and take cover against the corner of the wall that divides the grounds on the right from the descending road on the left. Hang just to the left a little so that you aren't visible to the janitor coming out to repair the pump. Just as he's reaching the pump, throw the gas can to your right so that it just barely tops the laundry hamper hiding spot. This will attract the janitor from inside the doorway to investigate. As soon as he's far enough that you can slip by, do so because you've got very little time.
Get into the building and immediately go for the door forward and to the right. This will put you in a hallway. The first door on your left will open to the guard station outside of the garage. There will be a guard just inside and to the right but he's busy or the door will block his line of sight (not sure which). Wait for the other guard to leave and you can grab the Evidence and the coffee mug from the table.
Leave this room and continue down the hall but stop before going through the door. There is a janitor on the other side of the door. Just wait for him to walk away from the counter. When he does, go through the door and then through the vent as usual.
On the other side, head to the right and wait for the man in the next room to move away from the door. Hug the left wall and transfer covers to get past the doorway with the people in the hall. Go up the stairs and use the checkpoint.
You have to restart the checkpoint now to reset the guard timers in the next room.
Take cover on the right door frame leading into the lobby. Listen to the conversation and just after the gay man finishes talking about how he'd rather be in the rain, transfer to the left door frame, take out your silenced silver baller and shoot diagonally across the lobby. Where? You are aiming across the far side of the room and through the open doorway over the shoulder of the guard. Don't shoot too closely to him because he will be aware that a bullet passed his shoulder. You want him to instead hear the sound of the bullet hit the wall behind him.
Give him a second to turn around, then come out of cover and take a step into the lobby. Hug the right wall until it takes you into the next hallway. Turn left and walk under the window of the control room. If you are on normal, go to the second doorway and curve into the control room. Wait for the guard to turn around and then slip over to the computer to use it. You will do this later if you are on hard.
Come out of the room, hug the right wall and jump into the vent before the guard finishes investigating the bullet shot. Cross the vent so that you drop into a laundry room on the other side. Come out of the door and turn left to find a guard at the end of the hall. Grab the film reel on the table ahead and to the left. As soon as you have it, cross the hall and hop into the closet. The guard will turn around and walk down the hallway.
As soon as he passes you, hop out of the closet (make sure you don't have a visible weapon) and go past where the guard was. Turn left and you'll enter the room with the projector. Stand in front of the projector, count to 8, and then turn the projector on. Take cover against the long side of the table nearby so that you are not visible to the guard on the other side. Wait for him to turn around and take a couple of steps so he can't see you and then exit the room through the other door on your left.
This will put you in a hallway. Walk up ahead and check to make sure nobody is coming in from the lobby because the female security guard may cross the hall right about now. Go up a little further to find the control room again. If you are on hard, slip in and use the coffee mug from earlier to distract one of the guards if you need to while you activate the computer. If there is a cop staring at the counter right next to the computer, he'll be fine and won't bother you.
Come out of the control room but stick to the wall just under the window or you'll be seen by the guard in the window. Slide down the far end of the hall and take the door into the lobby that you first entered. Take cover behind the couch and slide down a little ways. You need to move across the couches (when it is clear to do so) and shoot into the room with the checkpoint. Aim at the floor and it will lure a guard in. About this time is the only time that the guard will move away from the elevator so you need to get over there quickly.
Acrivate the elevator and then take cover behind the small section of pillar to your right. A guard or two may be returning so you need to be here to not be seen. As soon as the elevator arrives, get on to get to the next area.
This is VERY hard to do. It can be done on Hard, however. This is not my own strategy but that of a forum member on the Hitman forums named "No Kills Dude". He came up with this and I distilled the movements for guide consumption. Keep in mind that this is difficult to accomplish even for the most hardcore of hitman fans. It is very possible that this is a "Suit Only" strategy that was never intended by the developers to exist. Even with the strategy laid out, if you can manage to accomplish this then there is very little in this game that you can't do.
