This is a really basic question, but I find that I'm less clear on the matter than I'd like to be.
The matter at hand is the use of the final -n to denote movement.
I believe that I understand the important difference between
1. La viro iras en la domo
and
2. La viro iras en la domon.
The first sentence conveys a man who is in a house and is going somewhere within the house, while the second conveys that a man who is not in a house is going into a house.

My question has to do with situations in which it would not be possible to go INTO something, only TOWARD it. I'll use as my example a sentence from Teach Yourself Esperanto by Cresswell and Hartley.

1. Go to the door, please.
the translation given in the book as correct is:
1. Iru al la pordo, mi petas.

Would the final -n (I don't think it's still called the accusative when used to denote movement, but I may be wrong) ever be correct in this situation?
For example, would either of these be correct:

2. Iru la pordon, mi petas.
or
3. Iru la porden, mi petas.

Because I think I remember reading somewhere that the -n takes the place of a preposition. Am I confusing different uses for -n?

Please explain why yes or no.
Thanks for your patience and assistance.

Later edit: Rohan's explanation (below) covers what I said here, but much better.

Greetings!

Not being an expert myself, I looked PMEG up. This is what I came up with:

1. Apparently, when -n is used without any prepositions when referring to a place (which is in the form of a noun), it always carries the implication that you're going INTO that place.

Here's an example from PMEG:

'Morgaux mi veturos Parizon.'

Here, 'Parizon' signifies that you intend to go INTO the city (as I comprehend it).

So you can't use a naked noun+'n' to refer to movement TOWARDS something.

E.g. you can't say 'Mi volas iri la muron.' to mean 'I want to go to the wall.'.

You'll have to use 'iri al la muro' here. (Or 'aliri muron', though PMEG says it might be somewhat uncommon.)

So, 'Iru la pordon, mi petas.' would probably mean something like 'Please go INTO the door.', which is what a detective might say to you if you were The Atom, if he wanted the locking mechanism of a door to be examined from within.

2. 'Iru porden, mi petas.' is correct. Using the -n with locative E-adverbs usually indicates motion towards the location indicated by the adverb.

-> Mi iras hejmen. = I'm going home (I'm moving towards it).

According to me, however, 'Iru LA porden...' would be incorrect, as 'la', being an article, cannot stand before adverbs. It would be like saying 'Go the towards-door...'. (Of course, one cannot always say that what sounds absurd in English will also sound absurd if translated literally into Esperanto, but in this case, that does seem to be true.)

And to render irrelevant everything that I've written here so far, here's what you should refer to for a more complete discussion:

http://bertilow.com/pmeg/gramatiko/rolmontriloj/n/...

May clarity reign!

On a very generic sense, the -n ending can be used to get rid of a preposition when there would be no ambiguity. "Mi laboris tri monatojn" can substitute "Mi laboris dum tri monatoj"; "Mi pagis dolarojn" can be used for "Mi pagis per dolaroj", and so on.

Compare with "*Ni renkontiĝis la klubon". En la klubo? ĉe la klubo? antaŭ la klubo? More specification is needed.

If you keep the preposition, then it would be a mistake to add the -n ending, unless you wish to infuse a sense of movement and the preposition has a spatial reference, but does not provide movement by itself. "La kato iras sub la liton" means, roughly, "La kato iras al sub la lito". The cat was not under the bed but now it is there. Compare with "La kato iras sub la lito", the cat already is under the bed and it is "going" (it is moving).

If I remember correctly, the following prepositions do not accept the accusative ending: al, ĝis, de, da, dum, el, je, kun, laŭ, per, por, pri, pro, sen.

Because the accusative -n can be used as a substitute for any preposition, the meaning of the resulting expression can be ambiguous, but the context usually makes it clear. Thus iru la pordon would mean (normally) 'go to (i.e. towards) the door', whereas boru la pordon would mean 'drill into the door' (if fixing a hook for clothes, for example).