For a very long time, some have dared venture into the open ocean in search of new lands, how did they find their way. The Europeans, developed at some point the use of the sexton but prior to that, what was used? For example how did Leif Erickson reach North America?
Stars, sticking close to the land, maps and even winds. Then compass happened.
Leif Erickson and Co. could see land from the tops of the mountains in Ireland and then Greenland and so on. So they could easily (comparatively) sail there, without being lost.