The year is 14-something, and the place is Germany. You must guide a band of four adventurers, with nothing but noble intentions, along the road to becoming the most famous heroes in the land. It all starts... however you like. In this singular and unwonted game, you're not presented (at the start) with a quest, and you aren't told where to go and what to do. Hell, you're not even suggested what to do! At any time, you can go wherever you want and do whatever you want. If you've ever heard of "railroading" in RPGs, this is the absolute opposite.
It will probably be difficult for you to decide what to do at first, since there are so many options. The only way to learn how to survive in medieval Germany is to die trying. Since you're not forced into a path where the challenges are tailored at all times to your current abilities, you will die more often than in most RPGs. It's to be expected--save often! Every time you die, you'll learn, and eventually you'll devise a plan to progress in abilities, wealth, and fame without getting yourself killed. And for a long time afterwards you'll still be perfecting that plan and discarding old strategies.
It's best to discover all this by yourself. Try exploring all the places in town to see what you can do there--both during the day and at night. When you feel there's nothing new for you there, step outside the city gates. Just roaming the countryside will get you in trouble (read "adventure"), and you can go to other cities, villages, castles, monasteries, mines, caves, covens of witches or Satanists, dragons' lairs... If you get killed, restore a recent game and don't try that kind of thing again until you have what it takes. Keep gaining the necessary experience and wealth by returning to the easier tasks.
Characters' progress is tracked very differently from most RPGs. There are no levels or classes, only skills and attributes. And armour is both necessary and expensive. There are two kinds of "magic": praying to Catholic saints, and making--with costly chemical ingredients and by lengthy, hazardous processes--alchemical potions that you can drink, sprinkle on your equipment, or throw at your enemies, depending on the case. Pen-and-paper role-players who preferred the likes of RuneQuest over D&D will absolutely love this game.
The historical setting is the best part for many of us, not just history nerds; after all, the game is broadly set without any specific reference to historical persons or dates. Even so, medieval Germany is a terrific place for adventures: there are brigands, robber barons, corrupt bishops, Satanists, witches, fairies, demons, dwarves, dragons, and many more threats, because the game's milieu includes the superstitious beliefs of medieval Germans, rather than bare historical facts alone.
You are free to roam the country, but there is a grand quest you can endeavour to complete, if you want--you can postpone it indefinitely, or turn it aside at any time. If you've heard anyone say that this game has no plot or ending, I can assure you those are mistaken assumptions because nothing about it is revealed at the start of the game, contrary to most RPGs. Since even finding the first thread of this plot is part of the game, and you won't be ready to confront it until your group has progressed a great deal elsewhere, I won't say more about it.
This game is an absolute jewel, in my opinion, and one of the best computer RPGs in history. It's one of the most singular creations by Microprose, but is as good as any of their other titles in any genre. Some people may not like the lack of compulsory direction, but no RPG aficionado should miss this one.