Tunnels & Trolls (abbreviated T&T) is a fantasy role-playing game designed by Ken St. Andre and first published in 1975 by Flying Buffalo. The second modern role-playing game published, it was written by Ken St. Andre to be a more accessible alternative to Dungeons and Dragons and is suitable for solitaire, group, and play-by-mail/post gameplay.
Kenneth Eugene St. Andre is an American fantasy author and game designer, best known for his work with Tunnels & Trolls, the fantasy role-playing game he has authored and curated since 1975, and Wasteland, the 1988 post-apocalyptic computer role playing game. He has been an active member of The Science Fiction and Fantasy Writers of America since 1989 and in June 2018, The Academy of Adventure Gaming Arts & Design inducted St. Andre into its Hall of Fame.
This was the best-ever solo RPG game (I picked up the 5th Edition back in the early 80's as a kid), one I spent hours and hours playing since it was very simple to set up and play, and the solo game modules were really fun and well-written. The big advantage was it was far less complicated than D&D, and didn't take itself so seriously (the opening game module was Buffalo Castle, if that gives you an idea).
It seems like this game is pretty obscure (at the tip of the long tail, so to speak), but there are actually a large number of solo adventures that are really cool, if you were lucky enough to find them. I probably managed to find about half of them in various gamer bookstores (back when such things still existed). Now you’d have to acquire them directly from the publishers. Here are a few listed on the T&T Wikipedia entry:
Buffalo Castle by Rick Loomis Deathtrap Equalizer by Ken St. Andre Labyrinth by Lee Russell Naked Doom by Ken St. Andre Dargon's Dungeon by Michael Stackpole Weirdworld by Keith Abbott Overkill by Michael Stackpole Beyond the Silvered Pane by James & Steven Marciniak City of Terrors by Michael Stackpole Sorcerer's Solitaire by Walker Vaning Sword for Hire by James Wilson Arena of Khazan by Ken St. Andre Sewers of Oblivion by Michael Stackpole Sea of Mystery by Gienn Rahman Blue Frog Tavern by James Wilson Mistywood by Roy Cram Jr. Gamesmen of Kazar by Roy Cram Beyond the Wall of Tears by K. Martin Aul Captif d'Yvoire by Steven Estvanik The Amulet of Salkti by David Steven Moskowitz
Tunnels and Trolls is a rules light role-playing game. It is more focused on role play than detailed mechanics. If you're a rules lawyer or like to pour over a table after table, it's probably not for you. If you however like to role play at least as much as your combat, then you should be happy.
One thing to note, humor is baked into this game. It's in the rules, it's in the adventures. If you don't have a pretty good sense of humor, you also might not enjoy this so much. But for everybody else,. :-)
Ps, most people in the community play with either the 5th edition or deluxe edition rules. One nice thing about the game is that the additions are backwards compatible. So if you have the deluxe edition, which is what I'm using now, you can play any adventure from first to the current edition.