Warning Contains Spoilers...
While Indy is swanning around the Globe trying to uncover the mysteries behind the Great Circle, you will find things a lot easier if you can disguise yourself like the locals. During Indy's adventure you will be given access to disguises that allow you to get around the locations easily enough. However, there are 3 hidden disguises that will allow Indy to go behind enemy lines and enter restricted areas to search for those elusive safes. There are also areas where you will get money for punching fascists in the face.
Be careful though, the captains know their men and will spot you, tout suite.
Vatican Disguises
The Clerical Suit is given to you when you first meet Father Antonio and is unmissable. The Clerical Suit also has a key that will allow you to get around the Vatican buildings.
The Blackshirt uniform is very easy to miss but will help you get around the Vatican without any trouble at all.
Continue along the main story until you meet Gina Lombardi on a balcony as the Zepplin arrives.


After the cut scene you will need to slide down the rope towards Saint Peter's dome. Once at the bottom turn around and crouch through the hole in the fence.


Drop down and get into some fisticuffs with some fascists. The Blackshirt disguise will be on a bench in front of you. It will also have a Blackshirt key allowing access to otherwise locked areas.
Gizeh Disguises
Like the Vatican you will be given the Digsite outfit as part of the story.

If you are wanting to get your hands on the Wehrmacht Uniform and key head over towards the train tracks and the Northern restricted zone.

If you cross under the train tracks you will see a guard tower with a locked door.

The Wehrmacht Disguise is on the other side just out of reach.

Head around the back of the tower and you can climb up using your whip.

Shimmy around and punch out the guard. Drop down and the disguise is yours.
Sukhothai disguise
While you are up North in Voss' Camp stealing gold to pay for your breathing device you should grab the Royal Army Uniform. It's the only disguise in Sukhothai but it will make exploration so much easier.

If you head all the way to the top and approach Voss' from the left your boat will not be able to go any further and you will have to swim.

Its not very far but it's the easiest way in. Be careful of the guards and make your way towards the largest structure.

You will notice some guards in their undergarments, this is the spot.

You will see the Royal Army Uniform sitting on a table.
Now you will be free to explore Indiana Jones and the Great Circle to your hearts content without the worry of being spotted.