RHEM 3 or RHEM 3: The Secret Library is an adventure game from Knut Müller and Got Game Entertainment.

The player again arrives into the city of RHEM, with a note from Zetais who studied the artifact in RHEM 2: The Cave. Kales uses the note given by the player to unlock a gate leading to the inner area of RHEM. The game's overall plot is not fully revealed until the player comes back to this area after solving a large number of puzzles.

As stated in the game's title, in order to solve most of the major puzzles, the player must first find and enter a "hidden library", a jumble of rooms containing roll doors and books on shelves. The books themselves contain hints to solve the other puzzles.

The player's goal is to find 10 green crystals scattered throughout RHEM, much like the other two games, in order to unlock the passage to a black crystal.

A new puzzle to access an Easter Egg part of the game resides near the game's end, requiring the input of several scattered, hidden clues. When that's solved, a key to change the route for the player's tram can be retrieved, allowing an extra stop on the way out.

There, 4 concept pictures of the game and a new message from Kales can be found. It takes the input of 4 glyphs to access the message. Kales then states that a special, 5-pointed "Star key" will be needed to access more of RHEM, foreshadowing the series' later events.