The inside of the human body is dark and closed off—for the most part—from the world around it. This is usually an advantage. But when something goes wrong and surgeons believe they can fix it, they need to open up the body's barriers and see inside. The most obvious strategy—an incision long enough to give the doctor a clear view—comes with its own complications, which is why, for centuries, surgeons have been testing tools and techniques that allow them to see and work inside the human body without slicing it wide open.

It's only in the past 30 years, though, that they've actually gotten good at it.

At the most basic level, looking inside the human body might involve putting a tube in an existing hole to allow a little light in. Greek and Roman doctors made use of vaginal and anal specula. In the 1800s, one doctor inserted a tube into a urethra and used candlelight to try to get a better view. By the end of that century, after Edison produced his lightbulb, a Glasgow physician built a tiny bulb into a similar tube.

But it wasn't until the second half of the 20th century when fiber-optic threads brought brighter light into the caverns of the body. And later, tiny computer chip cameras started sending images back out. At last, doctors could not only clearly see inside a person's body without making a long incision, but could use tiny tools to perform surgery inside.

Since the 1980s, minimally invasive (or laparoscopic) surgery—in which a surgeon cuts a series of small incisions, inserts small, tubular tools, and uses those to operate—has become routine. There's even a robot, the da Vinci surgical system, that can perform minimally invasive procedures while the surgeon guides its many hands from across the room. (Its work has not been perfect, however.)

In the past few years, surgeons have been pushing to make these less invasive surgeries almost entirely invisible. Instead of cutting a tiny window in the outside of the body, they thought, why not cut one inside? Surgeons would first enter a person's body through a "natural orifice" and make one small incision, through which to access internal organs. The end result of this idea was that, in 2009, a surgeon removed a woman's kidney through her vagina.

Few surgeons were convinced this was actually an improvement though. Instead, they have focused on minimizing the number of tiny incisions needed to perform surgery. Single-site surgery requires just one "port" into a body.

A team of surgeons at Columbia, for instance, is working on a small robotic arm—minuscule, when compared to the da Vinci system—that can sneak into one 15 millimeter incision. And NASA is working on a robot that can enter the abdominal cavity through a person's belly button, Matrix-like, to perform simple surgeries. It's meant to be used in emergencies, but we know how this story goes: Soon enough, it'll be routine for a robot to slide into a person's body and pull her appendix back out.