The Dead Sea appears on virtually all modern maps. The question "Why is the Dead Sea not shown on a map?" stems from a classic dad joke:
"The Dead Sea was feeling depressed. Its friends thought a map would cheer it up, so they showed it where Jordan was."
The Dead Sea is a hypersaline lake bordered by Jordan (east) and Israel/West Bank (west). At ~430 m below sea level, it's Earth's lowest land elevation. Its name reflects its extreme salinity (~34%), which prevents most macroscopic life.
It puns on "Dead" (depressed) and "Jordan" (the country/river). Cartographically, the Dead Sea is prominently labeled—no mystery, just wordplay.