The map is not a relic of the past. Take careful note of the plotted course. Once you have your bearing, follow it as straight and true as possible. When your compass becomes useless, you’re close. When the sun never sets, just hangs high above, you’re closer. When you’ve sailed as far as you dare, you’re right there. Just a little further, you’re off the map now, and the edge of the world awaits.
Here the sea does not drain down into the void. It soars up and flows toward the sky becoming another sea with another world within it. Sailing from one sea to the other is difficult. The transition is a delicate balance as up and sideways turn around each other. Many ships have drowned or tipped or flipped. Get your speed up, race along the edge, turn into and up the wall of water. A good captain may still wet her sails on the bend.
Once past the edge, a world like, but unlike, your own awaits. Tropical islands, snow-covered islands, sandbars, vast coastlines of forests, deserts, swamps, mountains, and more. These lands are not for the taking. The people are friendly no matter how startling their appearance. In less than a day, you will forget about their third eye. In less than a week, you will overlook their fifth and sixth arms. In less than a month, you will be used to their armored skin. In less than a year, their claws will seem no different than your own fingernails.
Be cautious in the harbor cities you visit. Be wary if traveling over land for any distance. Thieves and pirates live on both sides of the bend. To be marooned here is to cast your fate into the sand. Native ships do not cross to your world. None from these lands will risk it. Your ship could make the return voyage if you can make the transition again.
But why would you leave? This world is a glory to behold. A captain could sail her whole life on this sea and gaze upon only a fraction of it all.
For the more adventurous, you need only remember a map has four edges.