Is "Cavidad Oscuro" actual Spanish, and if so, what does it mean?

Question

In something I once read a character was imprisoned in a place called a 'Cavidad Oscuro'- does this phrase have any actual meaning in Spanish or is it something the writer made up on the spot?

Answer 1

It's incorrect Spanish, as it does not respect the gender concordance ("cavidad" is feminine, hence it should be "cavidad oscura" = "dark cavity")

I see, googling, that "cavidad oscuro" is related with "Pena duro" (it should be "Peña dura"), another fictional place with incorrect Spanish. As it says here:

A former monastery, the Peña Duro (“Hard stone” - presumably Santa Priscan Spanish is different than mainstream Spanish)...

Answer 2

"Cavidad oscuro" is most definitely not Spanish. "Cavidad" is a femenine noun in Spanish, and so in order to keep a gender agreement it should be "cavidad oscura", which literally translates to "dark cavity" or "dark hole". That would make sense if referring to a cellar/dungeon/cell/etc.

• Cavidad (lat. cavitas): espacio hueco dentro de un cuerpo cualquiera. (=hollow space inside any body)
• Oscuro/a (lat. obscurus): que carece de luz o claridad (=lacking light or clarity)

On the other hand, maybe Oscuro is the name of something (which would explain why it is capitalized). In that case, it would be okay to say "Cavidad Oscuro". In Billy and Mandy, that Reaper guy was called Muerte, and if he had had a dungeon I guess he could have called it "Cavidad Muerte", so you can see you can just add a name to a noun to make a compound noun. Without farther context, that's all I can say.