The Tar Swamp is a location on Eternia. A young Prince Adam and Cringer once became stuck in it, and would have died if Orko hadn't appeared and saved them with his Magic Medallion (which he then lost in the swamp).
The Tar Swamp also contains the remains of many extinct creatures, including two Shriekers and a Drachadon that Skeletor once revived by using a Primeval Potion and then forced to attack the Royal Palace.