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"Spa" is a noun which is often translated as "spa", and "balneario" is a noun which is also often translated as "spa". Learn more about the difference between "spa" and "balneario" below.
el spa(
ehs
-
pah
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
el balneario(
bahl
-
neh
-
ah
-
ryoh
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
a. spa 
Este sábado me lo voy a pasar relajándome en el balneario.I'm going to spend this Saturday relaxing at the spa.
Este balneario ofrece baños con algas, baños con fango y piscinas termales.This spa offers seaweed baths, mud baths, and thermal pools.
b. health resort  (town)
Las aguas termales del balneario son beneficiosas para la salud.The health resort's hot springs are good for your health.
2. (tourist destination) (Latin America)
Regionalism used in Latin America: all the countries in South America, Central America, and the Caribbean. Does not include Spain.
a. beach resort 
Nos vamos de vacaciones a un balneario en el Caribe.We are taking a vacation at a Caribbean beach resort.
b. seaside resort 
De pequeños, siempre nos íbamos al mismo balneario.We always went to the same seaside resort when we were young.
An adjective is a word that describes a noun (e.g., the big dog).