Нет бы нам проверить номер этажа — мы приехали не туда.

Here нет бы is an idiomatic, conversational expression. It does not mean a literal no.

In this sentence, нет бы нам проверить номер этажа expresses regret, criticism, or annoyance about something that would have been sensible to do but was not done.

Depending on context, it can be translated as something like:

• we should have checked...
• if only we had checked...
• instead of that, we should have checked...

So the tone is roughly:
We should have checked the floor number — we ended up in the wrong place.

It often sounds mildly reproachful, either toward oneself or toward others.

That is a very common learner question.

It is true that in many basic patterns, бы combines with a past-tense form to make a conditional or hypothetical meaning, such as я пошёл бы.

But бы is also used in a number of fixed or semi-fixed constructions, and нет бы + dative + infinitive is one of them.

So in:

Нет бы нам проверить номер этажа

the pattern itself is idiomatic. You should learn it as a chunk:

• нет бы мне...
• нет бы тебе...
• нет бы нам...

It means something like you/I/we should have... with an emotional, complaining flavor.

So although бы often appears with past-tense verbs, it is not limited to that pattern.

Because in this construction, the person who should have done the action is usually put in the dative case.

So:

• нам = to us / for us
• мне = to me
• тебе = to you

This is normal in the нет бы + dative + infinitive pattern.

So:

• Нет бы мне спросить = I should have asked
• Нет бы тебе подождать = You should have waited
• Нет бы нам проверить = We should have checked

Using мы проверить would be ungrammatical here.

Because проверить is the perfective infinitive, and it fits the meaning here better.

The speaker is talking about one completed action that would have solved the problem:

• check the floor number once
• then avoid the mistake

So проверить means to check and complete the checking.

If you used проверять, that would be the imperfective form, which usually suggests process, repetition, or an ongoing action. In this sentence, that is less natural, because the point is not the process of checking but the missed single action.

So:

• проверить = to check once, successfully/completely
• проверять = to be checking / to check repeatedly / to check in general

This is a very common Russian noun pattern:

noun + noun in the genitive
to mean the noun of something

So:

• номер этажа = the number of the floor = the floor number
• номер комнаты = the room number
• крыша дома = the roof of the house
• цвет машины = the color of the car

Here the main noun is номер, and этажа tells you what number it is.

In English we often use noun-noun combinations such as floor number, but Russian usually expresses this with the genitive.

Туда means to there or in that direction / to that place. It is a directional word.

Там means there. It describes a location, not movement.

Because приехали is a verb of motion meaning arrived/went by transport, Russian uses the directional form:

• приехали не туда = we went/arrived to the wrong place
• literally: we arrived not to there

Compare:

• Мы не там = We are not in the right place
• Мы приехали не туда = We came to the wrong place

So with movement toward a destination, туда is the natural choice.

Приехали is the past tense plural form of приехать.

Breakdown:

• при- = arrival prefix
• ехать = to go by vehicle / to ride / to travel by transport
• приехать = to arrive by transport
• приехали = we/they arrived by transport

It is plural because the implied subject is we.

This verb suggests they got there by some means of transport: car, bus, taxi, train, etc.

If they had arrived on foot, Russian would more naturally use пришли.

Also, приехать is perfective, which fits the idea of a completed arrival: they ended up there.

The dash links the two parts in a sharp, expressive way:

Нет бы нам проверить номер этажа — мы приехали не туда.

It signals a strong connection between:

1. the missed sensible action
2. the bad result

The feeling is something like:

• We should have checked the floor number — and as a result we came to the wrong place.

The dash is very natural in Russian for this kind of emotional conclusion or consequence. It is more vivid than a plain conjunction.

You could paraphrase it with something more explicit, for example:

• Надо было нам проверить номер этажа, но мы приехали не туда.
• Надо было нам проверить номер этажа, и в итоге мы приехали не туда.

But the dash sounds more immediate and expressive.

Yes, especially because of нет бы.

The whole sentence sounds natural and conversational, like spoken Russian or informal written Russian. The speaker is complaining or criticizing the situation in a lively way.

A more neutral version would be something like:

• Надо было нам проверить номер этажа — мы приехали не туда.
• Нам надо было проверить номер этажа, но мы приехали не туда.

So if you use нет бы, it gives the sentence a more emotional, informal tone.

It can be broader.

Literally, не туда just means not to the right place / to the wrong place. The exact meaning depends on context.

Because the first part mentions номер этажа, the listener will probably understand that the mistake has something to do with the floor number. But не туда itself does not specifically mean the wrong floor only. It could mean:

• the wrong floor
• the wrong entrance
• the wrong building
• the wrong destination in general

So the context narrows the meaning, while не туда stays fairly general.