"Vacaciones" is always plural and the words that go together with "vacaciones" are plural, too. There's no singular form such as "vacation" in Spanish. Ejemplos (todo en plural, determinantes, adjetivos, etc.): ¿Cómo han ido las vacaciones? Nunca tuve unas vacaciones tan bonitas. Empiezo mis vacaciones la próxima semana.

It's plural, yeah, and I disagree, I've never heard the word "vacacion" in Spanish. I guess is plural because you understand you've been off for a bit rather than only one day. In Spain holidays are usually summer ones 15 or a bit less days, same Xmas and Easter so probably works like that. Let's think is like in English.. You also say holidays...

well, you're right, the singular form would be "vacación" is not widely use.however you might hear it.