El museo abre todos los días salvo el lunes.

Abre is the present tense of abrir and is very commonly used for opening hours, timetables, and routines.

• El museo abre... = the museum opens / is open
• El museo está abierto... = the museum is open

In practice, both can work in this kind of context, but they are not identical:

• abre focuses on the museum’s schedule or opening pattern
• está abierto focuses on its state of being open

So a notice about regular opening days often sounds very natural with abre.

Literally, abre means opens, but in sentences about business hours or public schedules, Spanish often uses abrir where English may prefer is open.

So in this sentence, abre todos los días is naturally understood as:

• it opens every day
• or more idiomatically in English, it is open every day

This is very common with shops, museums, banks, offices, etc.

Spanish usually uses the definite article much more often than English.

Here, el museo refers to the museum as an institution or place being talked about. In English, we also say the museum, so this part matches fairly closely.

In general, Spanish often prefers an article where English might sometimes leave it out in headlines or labels.

Both are possible.

• todos los días = every day
• cada día = every day / each day

In this sentence, todos los días is very natural and common for schedules and routines.

A few notes:

• todos los días often sounds slightly more everyday and standard in notices
• cada día can sometimes feel a bit more like each day, depending on context

For opening hours, todos los días is probably the most typical choice.

Salvo means except for or except.

So salvo el lunes means except Monday.

It is correct and natural, but it can sound a little more formal or written than some alternatives. Other common options are:

• excepto el lunes
• menos el lunes

All three are understandable, but:

• salvo often appears in notices or formal written language
• excepto is very common and neutral
• menos is common in everyday speech

In Spanish, days of the week usually take the definite article:

• el lunes
• el martes
• los lunes

So after salvo, it is normal to say salvo el lunes.

This does not necessarily mean one specific Monday only. In a sentence about a museum’s regular schedule, el lunes is understood as Monday as the weekly exception.

This is a very common question.

• el lunes = on Monday / Monday
• los lunes = on Mondays

But in schedule-style sentences, Spanish can sometimes use el + day in a more general way.

In this sentence:

• salvo el lunes means except Monday
• it refers to Monday as the exception in the weekly schedule

If you said salvo los lunes, that could also be understood, but it sounds more explicitly like except on Mondays as a repeated pattern.

Here, salvo el lunes is perfectly natural.

Because día is one of the exceptions.

It is a masculine noun:

• el día
• los días

So we say:

• todos los días
• not todas las días

The -a ending often suggests a feminine noun, but not always. Día is a very important exception to learn early.

The accent mark in día shows that the i and a are pronounced in separate syllables:

• dí-a

Without the accent, Spanish spelling rules would tend to treat the vowel combination differently.

So the accent helps show the correct pronunciation and stress.

Yes, absolutely. That is a very natural alternative.

Compare them:

• El museo abre todos los días salvo el lunes.
• El museo está abierto todos los días excepto el lunes.

Both are correct. The main difference is style:

• abre sounds like a statement of the museum’s opening schedule
• está abierto emphasizes the museum being open
• excepto is a bit more neutral and common than salvo

So your alternative is completely good Spanish.

The given order is the most natural one for a neutral statement:

• El museo abre todos los días salvo el lunes.

But Spanish does allow some variation, especially for emphasis. For example:

• Salvo el lunes, el museo abre todos los días.

This puts the exception first and gives it more emphasis.

For a standard notice or textbook sentence, the original order is the best model to learn first.

Yes. It sounds natural and correct in Spain.

A speaker in Spain might also say:

• El museo abre todos los días excepto el lunes.
• El museo está abierto todos los días menos el lunes.

All of these are normal. The original sentence is a bit neat and written in style, which makes it especially suitable for a sign, website, leaflet, or formal description of opening days.