Learn Italian: Il paese è abbandonato e non si avventura mai nessuno qui. - The town is abandoned and nobody ever ventures here.

This is called negative concord stacking. Because the negative words mai (never) and nessuno (nobody) come after the verb, Italian requires the main negative particle non before the verb. You can chain multiple negative words like this without canceling them out: it literally translates to "not ventures themselves never nobody".

Does the order of mai and nessuno matter after the verb?

Yes, usually adverbs of time like mai stay right next to the verb, while pronouns like nessuno follow them. Because of this rule, non si avventura mai nessuno sounds much more natural than swapping their order.

How would the grammar change if we put nessuno before the verb?

If a negative pronoun like nessuno comes before the verb, the pre-verbal non must be dropped. The clause would become e nessuno si avventura mai qui. Notice that mai still stays in its normal spot after the verb.

I thought paese meant "country". Why is it translated as "town" here?

Paese is a common dual-meaning word. It can mean "country" (a nation) or a small "town" or "village". Context tells you which one to use: an entirely abandoned nation is highly unlikely, so it must refer to an abandoned town here.