Learn Spanish (Spain): Visitamos muchas ciudades famosas en España.

Muchas means "many" and describes the noun ciudades (cities). Because ciudades is a feminine plural noun, the quantifier mucho has to change to match its gender and number, becoming muchas. You would use muy (very) only before adjectives or adverbs, not nouns.

How can I tell that ciudades is feminine if it doesn't end in -a?

Most Spanish nouns ending in -dad, like la ciudad (the city) and la universidad (the university), are feminine. To make it plural, we add -es because it ends in a consonant, giving us ciudades.

Why is the word famosas placed after ciudades?

In Spanish, descriptive adjectives like famosas (famous) usually come right after the noun they describe, rather than before it like in English. It also ends in -as to perfectly match the feminine plural noun ciudades.

Is visitamos in the present tense or the past tense?

In this sentence it means "we visit" (present tense), but it could actually be both! For regular -ar verbs like visitar, the "we" form is spelled and pronounced exactly the same in the present tense and the simple past tense. You just rely on context to know which one it is.