Learn Spanish (Latin America): En las vacaciones, viajamos mucho.

In Spanish, the word for vacation is almost always used in its plural form, las vacaciones. Because it is a plural noun, if you wanted to say you like vacations in this lesson, you would need to use the plural form gustan instead of gusta (for example, Me gustan las vacaciones).

Why does the sentence use en for on? Shouldn't it be something else?

In Spanish, en is a very versatile word that can mean in, on, or at depending on the context. When talking about periods of time or events like a vacation, en is the natural choice to mean on or during.

How do we know who is traveling if there is no word for we (nosotros) in the sentence?

The verb ending tells you exactly who is doing the action. The verb viajar (to travel) changes to viajamos for the we form. Because that -amos ending makes it perfectly clear, the pronoun nosotros can be left out.

Since las vacaciones is plural, why isn't mucho plural too (muchos)?