High security mechanical locks are designed with several conflicting goals in mind. With the proper key they must open reliably and with minimal effort, even after a decade of wear (tens of thousands of uses) and even if exposed to environmental hazards such as water and dirt. Without the proper key they must withstand manipulation by a skilled and dedicated adversary who may expend great effort to build specialized tools to attack a specific type of lock. They must withstand several minutes of drilling or other physical attacks. And any design meeting these requirements is worthless unless it can be built for a reasonable price.
I will describe some of the more interesting lock designs, and some of the creative attacks against these locks.