We're trying, with all our might, to avoid mention of final frontiers. Really we are. But, NASA's Voyager 1 is at the last point before crossing one. Currently the spacecraft is passing through what scientists are calling a "magnetic highway." This region is where the sun's magnetic field lines connect out to interstellar ones, which allows charged particles from our heliosphere (a surrounding cloud of charged particles encasing the sun) to pass out, while higher-energy particles from outside stream in. This area is still considered inside our solar bubble -- due to the lack of change in the direction of magnetic field lines -- but thanks to the ingress of external particles, it does give NASA a taste of conditions in deeper areas of the galaxy. Likewise, the agency believes this is the final... stage before reaching interstellar space, which it's estimated Voyager 1 will encounter in anything from a few months, to a couple of years' time.