A great example of a funhouse competition module, this was first played in 1979 in the AD&D competition at WinterCon VIII, at the time a limited edition for players attending the event was made available, but in 1980 we got this commercialized version of the module. Although this was now directed for people to play at home they did something cool with it making it a hybrid between a play at home and a competition module. TSR did this by distinguishing elements for use in the competition but adding optional encounters for use if you were playing casually which would extend the adventure. 

The adventure needed extending because the competition was meant to be finished in 3 hours, a bit short for a module. So in 1980, when you bought this you could choose how to play it. You get all the competition instructions as well as scoring and pre-made characters to make the whole thing fair, but if you just wanted to integrate it into your ongoing campaign you could also do that and use loads of extra encounters purposely created for that.

As a dungeon this is pretty much a puzzle-solving funhouse, you start off having to collect key parts to open a central door and each key is behind a puzzle that you need to solve to progress. After solving the key puzzles you go into the titular ghost tower which you need to ascend to get your prize. You go through levels representing the four elements and when you get to the top you get the Soul Gem you came here to find. Full of little games to solve, like the iconic reverse gravity fall into an upside-down sea, this is a real classic.