My favorite antique job was this 16^th century strongbox, probably of Carribean origin, painted with many tropical birds. The customer brought it in with the key, but it would not open.  The key would turn and I could feel the bolts being pulled back but the lid would not lift.

Once opened, the boltwork was covered by this intricate cutwork coverplate.

The key lock actually moved this complex boltwork which moved 5 individual active locking bolts.

The key, also visible in the first  two pictures, entered a covered keyhole, shown below closed.

Once I had the box opened I found that one of the lockbolt drivers had slipped past the spring and was no longer retracting the bolt.  A little TLC and gentle persuasion moved it back into proper alignment and the strongbox worked normally once again.