Learn Hardcore Icelandic: Við höfðum beðið þangað til pósthúsið opnaði. - We had waited until the post office opened.

It’s the past perfect (pluperfect): auxiliary höfðum (past of hafa) + the supine/past participle beðið. It marks an action completed before another past event—here, the waiting finished before the post office opened.

Could I also say "Við biðum þangað til pósthúsið opnaði"? Is there a difference?

Yes, that simple past version is also correct. The simple past neutralizes the sequence and just narrates events in the past, while the past perfect highlights that the waiting was already completed by the time of the opening or that you’re looking back from a later past vantage point. In everyday storytelling, both are common.

Why is "opnaði" in the past tense instead of present (opnar) or past perfect (hafði opnast)?

Because it’s the later past event anchoring the timeline; the earlier action takes the past perfect, and the later one stays in simple past: “had waited” → “opened.” Use present only when the main clause is present/future (e.g., Við bíðum þangað til pósthúsið opnar “We’re waiting until the post office opens”). Using a past perfect for the opening would incorrectly put it earlier than the waiting.

What does "þangað til" mean, and how does it compare to "þar til" or "uns"?

þangað til = “until” (temporal). Very common in speech and writing.
þar til = also “until.” Slightly more formal in tone; both are accepted today.
uns = “until” in a more literary/older style. All three can introduce a time clause; þangað til and þar til are the safest everyday choices.

Do I need "að" after "þangað til" or "þar til"?

No. You can say þangað til pósthúsið opnaði or þar til pósthúsið opnaði. Some speakers insert að (e.g., þar til að pósthúsið opnaði), but in careful writing it’s usually omitted. As a learner, prefer the versions without að.

Why is the order "pósthúsið opnaði" and not "opnaði pósthúsið" in the until-clause?

In these adverbial clauses, Icelandic typically keeps normal subject–verb order (a kind of embedded V2): subject first, then the finite verb: pósthúsið opnaði. Verb-first (opnaði pósthúsið) is used for yes/no questions or certain stylistic main-clause orders, not here. Also avoid þangað til opnaði pósthúsið.

Why is it "beðið" and not the infinitive "bíða" after "höfðum"?

After hafa, Icelandic uses the supine (often identical to the neuter past participle) of strong verbs. For bíða (to wait), the principal parts are:

Present: bíð
Past sg.: beið
Past pl.: biðum
Supine/past participle: beðið Hence: Við höfðum beðið.

Does "bíða" require "eftir"? How would I say “wait for the post office to open”?

You have three patterns:

bíða + genitive (a noun): e.g., bíða lestarinnar “wait for the train.” To use it with the post office opening, you’d say a noun phrase like bíða opnunar pósthússins “wait for the opening of the post office.”
bíða eftir + dative (a thing) / eftir því að + clause: e.g., Við biðum eftir því að pósthúsið opnaði “We waited for the post office to open.”
bíða with an “until” clause: Við biðum/ höfðum beðið þangað til pósthúsið opnaði. Saying bíða pósthússins by itself doesn’t mean “wait for it to open.”

What’s going on with the form "pósthúsið"? Why that ending?

pósthús is a neuter noun (“post office”). The definite nominative singular adds the article -ið: pósthúsið = “the post office.” It’s the subject of opnaði, so nominative is expected.

Any quick pronunciation tips for the special letters here?

Approximate guides:

þ as in English “th” in “thin.”
ð as in “th” in “this.”
á like the “ow” in “cow.”
ó like “owe.”
ú like “oo” in “food.”
ö somewhat like the vowel in British “bird.” Examples: Við ~ “vith,” þangað ~ “THANG-ath,” póst ~ “post” with long o, húsið ~ “HOO-sith,” opnaði ~ “OP-na-dhi.” (Very rough approximations.)

Can I front the “until” clause? Do I need a comma?

Yes: Þangað til pósthúsið opnaði, höfðum við beðið. A comma after a fronted adverbial clause is common and clear, though comma use varies by style. With the original order, no comma is needed.

What’s the difference between "þangað til" and "áður en"?

þangað til = “until,” marking an endpoint that you reach (often after waiting/continuation).
áður en = “before,” locating one event earlier than another. Compare: Við biðum þangað til pósthúsið opnaði (we kept waiting up to the opening) vs. Við fórum áður en pósthúsið opnaði (we left before it opened).

How do I say “not until”? Is it the same structure?

Use ekki fyrr en:

Við fórum ekki inn fyrr en pósthúsið opnaði. = “We didn’t go in until the post office opened.” This is different from using þangað til, which doesn’t include the negation.

Why "opnaði" and not "opnaðist"? Are both possible?

Both can be used intransitively:

opnaði (from opna) is fine for scheduled openings: Pósthúsið opnaði kl. 9.
opnaðist/opnuðust (middle voice -st) is common for things that “open by themselves” or as events: Dyrnar opnuðust. For a routine, timed opening, opnaði is idiomatic; opnaðist is possible but often sounds more event-like.

Is there another way to express “had finished waiting,” like English “were done waiting”?

Yes: vera búinn (búnir/búnar/búin) að + infinitive focuses on a completed result. For a mixed or male group: Við vorum búnir að bíða þangað til pósthúsið opnaði. With a female group: búnar; with a singular neuter subject: búið. This construction emphasizes being “done” more than the timeline relation that the past perfect gives.

Does "til" here govern the genitive? I don’t see any genitive after it.

Not in this expression. In þangað til, til is part of a fixed temporal linker meaning “until,” not the preposition “to, until” that takes a genitive object. So no genitive follows here.

Can I drop the subject "við"?

No. Icelandic is not generally a pro-drop language; subjects are normally overt. Keep við.