Module M2 "Maze of the Riddling Minotaur" by Jeff Grubb is an Expert D&D solo adventure for a 6th level character of any class (seven named, pregenerated characters are included).* A separate section alternately covers play for a party of adventurers.
*the banner on the cover stating character levels 1-10, notwithstanding
Title page to module M2 "Maze of the Riddling Minotaur" (1983) by Jeff Grubb. Illustration by Keith Parkinson.
The module was edited by Michael Williams. Illustrations were by Timothy Truman (cover) and Keith Parkinson (interior).
An invisible ink pen was used to reveal the hidden entries (also viewable using a blacklight). Individual entries are available here.
I found "Maze of the Riddling Minotaur" to be great fun, but needed to use more than one character to complete it (my first character was slain by harpies).
Design Origins:
"Maze of the Riddling Minotaur" was Grubb's pitch for an invisible ink module, shortly after he began working at TSR, as recounted in this interview.
The Moldvay Basic rulebook is cited by page number, although the module was published after the release of the 1983 version of the D&D Basic rules, edited by Frank Mentzer.
Grubb drew upon Greek mythology for inspiration, specifically the story of Theseus and the Minotaur, although with notable personal touches.
Location:
The adventure begins "in a sea-coast pub". Locations for the islands of Cathos or Vacros are not specified, although Michele Carpita (LoZompatore) exploits a "cartographic hole" in Another Vacros and Cathos placement theory.
Proposed locations for the islands of Cathos and Vacros, on the map in the D&D Companion Set (1984). The shaded boxed area represents the continent in module X1 "The Isle of Dread".
Kiranjo:
The bull-headed deity "Kiranjo the Minotaur" invites comparison with Gylgarid, another bull-headed deity, described as "a chaotic barbarian god of uncertain origin in the north" in module X13 "Crown of Ancient Glory" (1987) by Stephen Bourne.
New Monsters:
Golem (Obsidian), Pocket Dragon,* Sacrol,** Spider (Giant Hunting), Zombie-Minotaur.
*similar to pseudo-dragons in the AD&D 1e Monster Manual (1977) and the novel "Quag Keep" (1978)
**also appearing in module X9 "The Savage Coast" (1985)
Expanding the Adventure:
The Maze of the Riddling Minotaur takes place on the northern tip of a large island abandoned for centuries by civilized man. There may be greater treasure and adventure among the jungle ruins of the city, as well as in the volcanic highlands. Also, should the characters return with the princess, they will be given a small sailing ship as a reward, opening the way to further adventures ai sea, such as those in Dungeon Module XI —The Isle of Dread.
Maze of the Riddling Minotaur