Instructions
Play through the "Raiders of The Lost Ark" section of the game, making sure to collect all of the artifacts in the section. After this, return to the main hall of Barnett College (the game's hub world).
Go to Indy's Office. You will need to solve the puzzle here in order to get a key. To do so, you will need to reach the various chests in the room.
Use explosives on the back right corner of the room for a chest. Use a high jumping character on the shelves in the back for the second chest. Use a Scholar on the glyph panel in the back left corner of the room for the third chest. Use an explosive on the left side of the room for a fourth chest. Use a thuggie statue on the right side of the room to find the fifth chest. Assemble the chests in the middle of the room in order to find the key.
Climb the stairs in the main hall, and use the key on the door to the right to find the artifact room.
Enter the hole on the left side of the room in order to play the secret "Young Indy" level. By completing this level, you will unlock the Young Indy and Boy Scout characters.