Walk to the very last obstacle (the beginning of the rope slider part) of the assault course, then climb up the net and stand on the platform (where the rope slider is). Now, Walk to the edge as though you were going to use the rope slider but don't...

When you are right at edge, sidestep (R2) to the right until you can go no further, and you should be touching the wooden wall on the right. Now, angle yourself towards the main wall of the Mansion, as if you were going to attempt to jump over to it - but don’t jump yet - you'll miss it!

Now this is the strange part. Jump (without pressing any directional keys) up and down a few times, and before you know it you'll be on top of the tower. This does take a little practice, but before you know it you will end Up on top of the tower-and therefore easily able to jump on to the wall! I’m not sure How you just end up on the tower-you just do!

Must be some kind bug or something-but it’s fun! You can now follow the outside wall to the front door, where you can jump down and explore the surroundings. Be warned that once you jump down, you'll have to restart the game because there is no way to get inside again.

You can also take a look at the mansion from some great angles, you can get on top of the swimming pool, and take a good look at the maze part.