There are many reasons you might want to physically destroy a hard drive rather than use disk wiping software: higher confidence that the data is destroyed, a recourse if your drive has failed and no longer accessible, and sheer fun.
If the pyrotechic/thermite method and other extreme physical disposal methods aren't for you, dismantling the drive to get to the platters is an alternative method. (You can also save some interesting parts from the drive — motors and magnets — for some geeky future projects yet to be invented.)
DominoPower Magazine has a step-by-step guide with photos of the process. You'll need a needle-nose plier, a flat screwdriver and TORX bits (for removing the star-shaped screws and bolts).
The basic process involves removing the screws around the outside of the drive (including ones hidden under stickers), pulling out the screws holding the electronics (including hidden case screws), and then popping the cover off. After removing the magnets, you can get to the platters, the heart of your hard drive.
First run the magnets over the platters to degauss them. Because that's not a guarantee that the data is unrecoverable (and not very satisfying, either, after all that dismantling), you should then physically destroy the platters — bend them or break them with a hammer or saw them into pieces. And that will be the end of those discs and the data on them. Check out the full instructions via the link below. Photo by Jon A Ross
Note: if you're looking for software solutions and more of an overview of secure file deletion, see our guide to properly erasing your physical media. What's your preferred method of disk destruction?
How to destroy a hard drive (on purpose) [DominoPower Magazine]