Without Debug mode, explore the Grounds thouroughly
When you go outside to the grounds, go to Hagrid's hut. When you are in the pathway, right when you start to see the dirt path, immediately turn right. Run up the slanted dirt area, and jump right before you can't go any farther into the dirt. If you jumped good enough, you will just stand on a thin line of dirt. Walk to your right, and jump. There will be an invisible box that you can jump on right next to the fire torch on the left. Then jump on the cement platform above. This allows you to go on most of the unused land on the grounds area.
More tricks, tips and cheats for this game are right here - Harry Potter and the Chamber of Secrets cheats