Si hubiéramos salido más tarde, habría sido difícil encontrar sitio en la barra de ese bar.

Because in Spanish, after si in this kind of unreal past condition, you normally use the pluperfect subjunctive:

• si hubiéramos salido más tarde = if we had left later

The result clause then uses the conditional perfect:

• habría sido difícil = it would have been difficult

So the pattern is:

• Si + pluperfect subjunctive, conditional perfect
• Si hubiéramos salido..., habría sido...

English uses if we had left..., it would have been..., and Spanish works similarly, but it does not use habríamos after si here.

It is the pluperfect subjunctive (also called the past perfect subjunctive).

It is made with:

• hubiera / hubieras / hubiera / hubiéramos / hubierais / hubieran
• • past participle

So here:

• hubiéramos
  • salido
• literally: we had left in a hypothetical/unreal context

This tense is commonly used for unreal past situations:

• Si hubiéramos salido antes, habríamos llegado a tiempo.
• If we had left earlier, we would have arrived on time.

Yes. Hubiéramos and hubiésemos are both correct.

They are two standard forms of the imperfect/pluperfect subjunctive series:

• si hubiéramos salido
• si hubiésemos salido

There is no important difference in meaning here. In Spain, both are common, though some speakers may personally prefer one form over the other.

It is the conditional perfect.

It is formed with:

• habría / habrías / habría / habríamos / habríais / habrían
• • past participle

So:

• habría sido = would have been

This tense is used for the result of an unreal past condition:

• Si hubiéramos salido más tarde, habría sido difícil...
• If we had left later, it would have been difficult...

Because after difícil, Spanish very often uses an infinitive directly:

• Es difícil encontrar sitio.
• It is hard to find a place/spot.

So:

• habría sido difícil encontrar sitio
• it would have been difficult to find space / a spot

You can sometimes see structures with de, but here the most natural wording is the direct infinitive:

• difícil encontrar

Here sitio means space, room, or a spot/place to stand or sit, depending on context.

In this sentence:

• encontrar sitio en la barra
• literally: to find space at the bar counter

It does not necessarily mean a reserved seat. It usually means there was enough room to get a place at the bar.

In Spain, sitio is very common in this sense:

• No hay sitio. = There’s no room.
• ¿Hay sitio en la barra? = Is there space at the bar?

La barra is the bar counter: the long counter where people stand or sit to order drinks.

So:

• en la barra de ese bar
• at the counter in that bar

This is especially natural in Spain, where estar en la barra often means standing or having a drink at the counter, not sitting at a table.

Spanish demonstratives depend on how the speaker sees the distance, whether physical or mental:

• este = this
• ese = that
• aquel = that over there / that one further away

So ese bar means that bar. It suggests the bar is not right here with the speaker as this bar, and not especially distant as that bar over there.

In real speech, the choice can depend on context, not just physical distance.

Because Spanish usually leaves out subject pronouns when the verb form already shows the subject.

• hubiéramos salido already clearly means we had left
• so nosotros is unnecessary

You could say:

• Si nosotros hubiéramos salido más tarde...

But it usually sounds more natural without nosotros, unless you want emphasis or contrast.

Because salido is a past participle, and with haber it does not agree with the subject.

So:

• yo habría salido
• nosotros habríamos salido
• ellas habrían salido

The participle stays the same: salido

This is different from forms used with ser/estar as adjectives, where agreement can happen:

• La puerta está cerrada
• Las puertas están cerradas

But with haber in compound tenses, no agreement:

• hemos salido
• habían salido

Because más tarde means later, which is the comparative idea needed here.

• tarde = late
• más tarde = later

So:

• Si hubiéramos salido más tarde
• If we had left later

If you said si hubiéramos salido tarde, that would mean if we had left late, which is a different idea.

Yes. This is the Spanish equivalent of the English third conditional, used for unreal situations in the past.

Pattern:

• Si + pluperfect subjunctive, conditional perfect

Example from your sentence:

• Si hubiéramos salido más tarde, habría sido difícil encontrar sitio...

English equivalent:

• If we had left later, it would have been difficult...

It talks about something that did not happen and imagines a different past result.

Yes. Spanish can reverse the order:

• Habría sido difícil encontrar sitio en la barra de ese bar si hubiéramos salido más tarde.

This means the same thing.

When the si clause comes first, Spanish normally writes a comma before the main clause:

• Si hubiéramos salido más tarde, habría sido difícil...

When the main clause comes first, a comma is often omitted:

• Habría sido difícil... si hubiéramos salido más tarde.

The accents show the correct stress.

• hubiéramos is stressed on -é-
• habría is stressed on -í-

These accents are part of the standard written forms and should always be included.

They also help distinguish pronunciation and, in some cases, verb forms.

Not if you want the same meaning.

• habría sido difícil = it would have been difficult
• sería difícil = it would be difficult

Your sentence is about a hypothetical situation in the past, so the natural form is:

• habría sido difícil

If you use sería difícil, it sounds more like a present/future hypothetical rather than a completed past one.

Yes, it sounds very natural in Spain.

In Spain, people often talk about:

• tomar algo en la barra
• ponerse en la barra
• encontrar sitio en la barra

It reflects the common social habit of standing or gathering at the counter in bars. So this phrase is not just grammatically correct; it is also culturally very natural in Peninsular Spanish.