"Eles foram à ópera ontem."

Translation: They went to the opera yesterday.

[Oinophilos]

How would you say "They were at the opera yesterday"?

[Paulenrique]

"Eles estavam/estiveram na ópera ontem".

[lugosky]

How do you know when to use '...para a/o...' vs '...à/ao...'

[Paulenrique]

ir a = to go for a short time

ir para = to go for an extended period of time, to move.

[4oYBIxtO]

"à ópera" sounds like "ao ópera" in both the male and the female fast voice