The only thing standing in the way of completing the famous Pan-American Highway is the Darien Gap, which has been too dangerous to penetrate for decades and remains the missing link to this major road. Anyone who wishes to travel from Panama to Colombia must fly or take a boat, as there's no way you can make the journey by land, unless you have a death wish.
For years, the area has been inhabited by Colombian paramilitary, hostile tribes, dangerous wildlife, and questionable terrain, making it one big danger cocktail. Some adventurers have made the treacherous journey, but others haven't gotten to the other side alive. Though paramilitary activities have calmed down a little in recent times, we still wouldn't risk a sudden kidnapping or a meeting with a territorial tribe. Try visiting one of Panama or Colombia's safer national parks instead.