You have to use time indicator with simple past because when you use simple past you are talking about finished actions and time, when they happened. So "I was in Spain last July". It is a story about your past. But you can look at the same travel to Spain in a different way. Imagine that you meet a Spanish person you want to impress and you tell this person "I have been to Spain!" meaning "I know your country". So simple past uses time indicators because it looks at the past from this exact point of view - as the past, but you can always decide "Maybe it was in 1998, 10 years ago but it still matters to me, it is still important" and then you will say "I have been to Spain" - you will use present perfect without any time indicator. But if someone asks you about the time when you were there, about details you will use past simple again. This much about simple past. Hope it helps a little.
You are Spanish! I have been to Spain.
O, it is great that you know my country! When were you there?
Last year, in July.
Where were you in Spain, in Barcelona? etc.
Student or Learner