Maris Profondus was most likely a sea, near Maris Cristallus and the Archipelago Ridiculus. This sea was supposedly explored by Gilderoy Lockhart who wrote about his "adventure" in Travels with Trolls. This expedition was, however a feat stolen by Lockhart from another wizard, which memory was erased. Maris Profundus was included on the map featured on the cover of Travels with Trolls.
- "Mare maris" means "sea" in Latin. "Profundus" is Latin for "deep"; "profound"; "boundless".
- Harry Potter and the Chamber of Secrets (film) (First mentioned)