There's a large museum called the National Museum of Japanese History (国立歴史民俗博物館) in my prefecture, just north of Tokyo.

NOTE: Many readers might want to *where* the museum is.

MORE PRECISELY: It consists of six galleries and it takes timeat least ** hours to look around all of them.

The original was vague; a more precise is better.

In the sixth gallery, you can see the[some] modern items.

For example, you can see inside of Japanese houses or popular magazines or anime things infrom the 1900s.

I [paricularily] like the first and sixth galleryies.

There's a large museum called the National Museum of Japanese History in my prefecture.

It consists of six galleries and it takes tima while to look athroundgh all of them.

Suggests that it's a long time. You can also say it "takes some time" or "quite a bit of time" to look through them

In tThe first gallery, you can see displays very old historical thingitems, and in the second gallery, displays items that are a little bit newer (compared to the first gallery).

Parallel sentence structure to make it flow better.

In the sixth gallery, you can see the most modern items.

For example, you can see the inside of a 1900s Japanese houses, or popular magazines or anime things in 1900s.

A Museum of Japanese History Museum

"Japanese history museum" sounds more general, which is good because you used the determiner "a" here instead of "the" which is a lot more general. This is a pretty minor correction, but I feel like its good.

If there was one specific main japanese history museum that everyone knew about or was the main place people went to though, "The Museum of Japanese History" or "The National Museum of Japanese History" etc. could be good.

There's a large museum called The National Museum of Japanese History in my prefecture.

It consists of six galleries and ithat takes time to look around all of them a while to get through.

or maybe "It consists of six galleries that each take a fair amount of time to get through."

Your sentence is not inherently wrong. These are just some nice alternative ways of saying it that I feel flow better.

In tThe first gallery, you can see features (replicas/models of) very old historical thingobjects, and in the second gallery, display items are a little bit newer compared to the first gallery has (models of) slightly more recent items.

this is really hard to correct, its not your fault though, just, as the corrector many assumptions have to be made.

In the sixth gallery, you can see'll find exhibits from the modern itemsera.

For example, you can see insidethe interior of Japanese houses, or popular magazines orand anime things in, all from the 1900s.

I like the first and sixth gallery.

This could be interpreted as you only liking the first and sixth gallery and not any of the other ones. You might consider putting "the most" on the end, so "I liked the first and sixth gallery the most."

There's a large museum called the National Museum of Japanese History in my prefecture.

It consists of six galleries and it takes (a lot of / quite some) time to look around all of them.

In the first gallery, you can see very oldancient historical things, and in the second gallery, display items are a little bit newer compared to the first gallerymore recent in comparison.

In the sixth gallery, you can see thmore modern items.

In this sentence "more" doesn't mean "additional".

Instead, it is being used as a comparison word with the previous sentence.

Sort of like this:
"The sixth galley has items which are 「more modern」 than the first gallery"

For example, you can see inside of Japanese houses or popular magazines or anime things infrom the 1900s.

I like the first and sixth gallery best.

There's a large museum called the National Museum of Japanese History in my prefecture.

In the first gallery, you can see very old historical things, and i. In the second gallery, the displayed items are a little bit newer compared to the ones in the first gallery.

In the sixth gallery, you can see the modern items.

For example, you can see insidethe interior of Japanese houses or popularfrom the 1900s, as well as magazines orand anime things in 1900sat used to be popular.

In Japanese, you wrote １９００年代の日本の家の中の様子とか, so I think you mean only the houses are from the 1900s. If 1900s is at the end of sentence, it sounds like you're saying that the houses, magazines, and anime things are all from the 1900s. But I think you're talking just about the houses from the 1900s, so I changed it.

I also changed "popular" to "used to be popular" because you're talking about magazines and anime that were popular in the historical past.

I like the first and sixth galleryies.

There's a large museum called the National Museum of Japanese History in my prefecture.

In the first gallery, you can see very old historical things, and i. In the second gallery, the display items are a little bit newer compared to the first gallery.

In the sixth gallery, you can see thmore modern items.

For example, you can see the inside of Japanese houses or, popular magazines, or anime things infrom the 1900s.