Learn Italian: I turisti hanno visitato il museo oggi. - The tourists visited the museum today.

Nouns ending in -ista are identical for masculine and feminine only in the singular (il turista vs. la turista). In the plural, they behave like regular nouns: masculine becomes -i (i turisti) and feminine becomes -e (le turiste). Here, the masculine plural i turisti is used for a group of male tourists or a mixed-gender group.

Why do we use avere (hanno) as the helper verb for visitare?

Visitare (to visit) is a transitive verb, meaning it takes a direct object. You are visiting something (in this case, il museo). Verbs that act directly on an object almost always use avere in the passato prossimo.

Since the subject is plural (i turisti), why doesn't the past participle change to match it, like hanno visitati?

When a verb uses avere as its helper verb, the past participle doesn't change to match the subject. It stays in its default -o form (visitato). You only make the participle agree with the subject when the helper verb is essere.

Could oggi go somewhere else in the sentence?