This puzzle came as a gift to me from another well known puzzle designer Goh Pit Khiam (thanks very much Pit Khiam!). The Keyhole is available from various online retailers including Amazon and Torito, however the latter doesn't ship internationally.
The Keyhole consist of two similar looking "maze" plates, resembling the jagged edges like the teeth of a key, which are interlocked together in the starting position. Object is to separate the two plates, via one of the openings on one of the plates. The Keyhole can perhaps be considered a much more difficult cousin of the Cast Key. Quality and finish is good and the Keyhole has a shinny finish. Usually I don't quite like polished surfaces, but for this puzzle, it looks fine.
Its not a very difficult puzzle by any means and Hanayama rates it 4 out of 6 stars in terms of difficulty (ie fairly hard). But the Keyhole is not as straight forward as it may appear to be at first. In fact, Hanayama states on its site (translated from Japanese) that the Keyhole is a "3-dimensional" maze. Not sure tho' if "3-dimensional" is stretching it a bit here.
As you play with the puzzle, you will discover that you need to shift the orientation of the pieces relative to each other to move the pieces towards the opening. But as you progress, some of the positions may result in a dead end. However with some persistence, eventually the plates will come apart. I was fiddling with the puzzle for several minutes trying this and that, and suddenly, one plate just came out and it was solved.
A nice addition to the very extensive Cast collection. And as with the Cast puzzle series, value for money.