There was a map made in the 1500s by a mapmaker named Piri Ries that he made as a copy from maps much older than his. His map shows Antarctica before it was covered with ice with such accuracy it wasn't until in the 1950s that we could verify his map because before that no one had to tools to look down through the ice to see what was under it.
We can see the Piri Reis Map bears no resemblance at all to Antarctica. The 600-mile wide Drake Passage is not shown, nor are the large islands in the Weddell Sea. The latitude is thousands of miles off.
So in response to people who ask how to explain why the Piri Reis Map shows the coastline of Antarctica accurately, the answer is - it doesn't. It especially doesn't show the subglacial coastline of Antarctica, which corresponds to the existing coastline of Antarctica around most of the continent anyway.
Source: https://web.archive.org/web/20130813090645/http://www.uwgb.edu/dutchs/PSEUDOSC/PiriRies.HTM