Learn Russian: Вы когда-нибудь ездили в круиз? — Нет, я никогда не ездил в круиз. - Have you ever gone on a cruise?

This is a classic example of the general factual use of the imperfective aspect. When asking if someone has ever done something, you are focusing on the experience or fact of the action itself existing in their life, not a specific result or a one-time completed action. Therefore, Russian uses the imperfective.

Could I use the unidirectional verb ехали instead of ездили in this sentence?

No. Ездили is a multidirectional verb, which in the past tense implies a round trip (going and returning). When combined with the general factual meaning of an experience, you need this multidirectional verb. If you asked Вы ехали в круиз?, it would mean "Were you on your way to a cruise?"

Why is it в круиз and not на круиз? Isn't a cruise an event or activity?

It can be tricky! While many events or activities take на (like на концерт), круиз traditionally takes в. You can think of it as taking the same preposition as traveling into a journey or voyage (в путешествие, в рейс). Because it expresses motion towards a destination, it is in the accusative case.

Why do we use когда-нибудь for "ever"? Could I use когда-то?