The majority of challenges in an adventure game are conceptual: puzzles that can only be solved by lateral thinking. The following list of a few popular puzzles—of the many types available—will help get you started:
■ Finding keys to locked doors. Locked door refers to any obstruction that prevents progress and a key is any object that removes the obstruction. Because this type of puzzle is so common, the challenge for you as a designer is to give players enough variety that the door-and-key puzzles don't all seem the same.
■ Figuring out mysterious machines. This is, in effect, a combination lock instead of a lock with a key. The player manipulates a variety of knobs to make a variety of indicators show the correct reading. Try to make the presence of these knobs reasonably plausible—too many adventure games include mysterious machines that clearly function only as puzzles, not as realistic parts of the game world.
■ Obtaining inaccessible objects. In this kind of puzzle, the player can see but not reach an object, which may be a treasure or a key to open some door elsewhere in the game world (remember that this doesn't need to be an actual key). The player must find a clever way of reaching the object, perhaps by building some device that gives her access.
■ Manipulating people. Sometimes an obstruction is not a physical object but a person, and the trick is to find out what makes the person go away or lets the player pass. If it's a simple question of giving the obstructor something he wants, then the problem is really just a lock-and-key puzzle. For a more creative approach, create a puzzle in which the person must be either defeated or distracted. The player should have to talk to him to learn his weaknesses.
■ Navigating mazes. Use mazes—confusing areas that make it difficult for the player to know where she is or where to go—sparingly. Making a bad maze is easy; making an interesting maze is difficult. A maze should always contain clues that an observant player can notice and use to help her learn her way around.
■ Decoding cryptic messages. Many players enjoy decoding messages, as long as you give sufficient clues to help out.
■ Solving memorization puzzles. These puzzles require the player to remember where something is—a variant of the game Concentration. She can usually defeat these by taking notes, but that's reasonable enough; it's how we remember things anyway. The real challenge for you as the designer is to create a realistic reason for a memorization puzzle to be in the game.
■ Collecting things. The player must find a number of objects. These may be the scattered pieces of a larger object, a set of related items (such as 12 identical gems), or simply miscellaneous treasures. Make the player meet challenges to reveal or retrieve these items; simply finding and picking them up isn't really a challenge.
■ Doing detective work. Instead of solving a puzzle per se, the player figures out a sequence of events from clues and interviews with witnesses. The situation doesn't necessarily have to involve a crime; you could use any unknown event. Detective work forms the basis for many police-procedure games.
■ Understanding social problems. This doesn't refer to inflation or unemployment. The challenges of understanding and perhaps influencing the relationships between people make up a little-explored aspect of adventure game design. Most adventure games limit characters to very simple, mechanical states of mind. If we devote a little more effort, people, rather than objects, could become the primary subject of adventure games, and this would make the games much more interesting.
When designing puzzles, try to allow for lateral thinking of the players. If there's more than one way to solve a puzzle, don't arbitrarily restrict the player to your preferred method. Obviously, you can't build in multiple solutions to every puzzle, but if the player tries something entirely logical and there's no good reason why it doesn't work, she's going to be frustrated. Only play-testing can tell you whether a puzzle is too hard or too easy, and you can't adjust an adventure game's difficulty by tweaking some numbers the way you can adjust the difficulty of games in some other genres.