Cheatcodes
Find the default.cfg file. Go to GameData/indy/default.cfg and edit it using notepad. (Be sure to back it up first)

Change the file to read as follows:

pack:0
title:0
freescenedata:1
vsyncinterval:2
milessound:1
nocontrol:1
cheats:1
resmgrload:res.dat
fullscreen:1

Save the file and run the game.

You will now have access to the builtin cheat mode with the following cheats:

Unlimited Health
Unlimited Oxigen
God Mode
Unlimited Ammo

Secret area:
On the first level when you first encounter crocodiles, kill all of them with your machete. Then, swim to the left next to the entrance to the temple. Swim behind the waterfall to pull up on a small ledge. You will not be able to see much, there is a box here. Break it open to get a bundle of dynamite.

Art gallery:
Collect all artifacts in the game to unlock an art gallery.

Bonus levels:
Enter the game director and enter the folder that contains its levels. Run the "ropetest" and "whipgym" files to play those levels, which are not found in other versions of the game.