What is the collective noun of visitors?

There isn't one universally accepted collective noun for visitors.

Here are some options, depending on the context:

Formal:

* A group of visitors

* A party of visitors

* A throng of visitors (suggests a large number)

Informal:

* A crowd of visitors

* A stream of visitors

* A bevy of visitors (suggests a charming or attractive group)

You can also use a more descriptive phrase like "a tour group of visitors" or "a gathering of visitors".