“Turn back, Fox, you’re too far!” “You cannot go that way, traveler. Turn back.” “Go back to the battlefield or else.” “10… 9… 8…”

Designing a game means defining limits to player interactivity, the kind of limits that any gamer will try to break. Thrashing across the edges of space and crawling over walls has become standard operating procedure for any curious character, prompting the kinds of messages seen above – reprimands from the haggard developer plugging the holes in the dam of player autonomy.

But as the player’s sugar-high of exploration wanes, the developer’s eyes widen in opportunity. It’s a player heading towards the end, towards the castle, the scripted explosion, and the months of programming and artwork that went into levels 2 through 10. An obstacle is born.

“The invisible wall” has been a necessary if undesirable constraint for game developers since the first 8-bit sprites were doomed to rightward travel. If these boundaries are a gamer’s bumpers then the intended obstacles are the bowling pins, often in the form of enemies and goals (see goombas, finish lines). It’s in the act of bowling - to stretch a smoky metaphor - and the skillful release that any game’s heart lays. You know, “joy in the journey,” “life’s not a destination,” et cetera.

Enter visible walls.

In the emerging era of sandbox gameplay (for which developers have only scratched the polygon-loaded surface), a game’s setting is itself a meaningful obstacle. The medieval form of the obstacle is the ubiquitous lock and key - skeletal, mythical, or otherwise. Originated by Adventure on the Atari 2600 (also known for the first ever “easter egg”) and widely propagated by a princess and her green-hooded hero, among others, keys began a tradition of object-oriented walls with inanimate solutions. Fleshy, wriggling keys followed to mild unease.

Innovation struck as keys became characters, even ideas. Convince the old soothsayer to let you into the Dark Canyon by proving you are the true hero via the mysterious song of the dragons, or something. Don a hulking diver’s suit to kidnap slug-impregnated girls who use crawlspaces to open doors, or don’t. Keys begin to take on meaning outside utility.

The developer’s keychain then grew with integrative, multi-use items. Open-world adventures like Arkham Asylum and Darksiders drip with the stuff. A simple, crucial door can be opened only with a cryptographic sequencer, attained after climbing to new heights with the batclaw, attained by blowing into a lair using explosive gel, and so on. The keys, or equipment, conspicuously slide round pegs into round holes marked “Round Holes for Round Pegs” - not subtle enough to lull the attentive gamer into soft immersion.

But one stone of game wizardry remained yet unheralded: the puzzle. It’s as antique as it can be fresh, insightful, and engaging. The player who accepts Chell’s role and allows for Aperture to create deployable portals reaps the harvest of core gaming’s purest intellectual delight. Dr. Mario diagnoses a strict, unadorned regimen of puzzles for the dormant mind. Detective Cole Phelps calls upon his powers of yelling-all-the-time and gesture deduction to snag that desk promotion. Variety only helps.

The loud majority of shooter fans may deride the relic of puzzles, touting Michael Bay-isms, a slick presentation, and twitch gameplay as the medium’s natural evolution. I ask, “Is there any greater FPS satisfaction than flanking the sniper’s nest, outwitting the twitchers with tactical (see: mental) prowess?” A user-navigated puzzle like this reluctant shooter scenario is the purest form of gaming’s visible walls. The player assumes dual roles – participant and developer – guided only by the bumpers that enclose and comprise the game.

While multiple solutions to complex puzzle systems aren’t a necessity, the freedom they engender is the calling card of an insightful designer. Not only are his invisible walls secured, but his visible walls are the center of the player’s rippling pond. And when the waves find their end, I am a smarter, happier gamer for it.