Learn Italian: Avessimo preso il volo con lo scalo! - If only we had taken the flight with the layover!

This is an independent exclamative subjunctive. Starting a sentence directly with the past perfect subjunctive is an emphatic way to express a strong regret or unfulfilled wish about the past. It translates naturally to 'If only we had taken...'. You do not strictly need a trigger word to convey this feeling.

What happens if I use the imperfect subjunctive (prendessimo) instead of the past perfect (avessimo preso)?

The meaning changes to a present or future wish. Prendessimo il volo con lo scalo! would mean 'If only we were taking the flight with the layover!' (for example, if you were currently booking the tickets). Because this sentence expresses regret over a missed opportunity that is already in the past, you must use the past perfect subjunctive.

Why is the article lo used in lo scalo?

Just a quick refresher from earlier levels: masculine nouns starting with s plus a consonant (like sc-alo) always take lo instead of il, and uno instead of un. So you will always see lo scalo or uno scalo.

What exactly is a scalo in travel contexts?