The cafe is located is at the beginning of the river Okutama valley , and the natural scenery is fantastic.

Among them, one person, a student from Budapest, stayed at a share-house near the cafe and helped with the construction.

The garden is still under development, but there are several art pieces that presented by a craftsman, and i. Inside the cafe, paintings by his female acquaintance, who areis a top-notch painters, adorned the walls.

There is another large painting still in progress, but it seems sthe artist will come from Osaka to stay for a week in May to complete the painting.

The cafe is located is at the beginning of the river in Okutama valley and the natural scenery iwas fantastic.

Is the cafe and river located in Okutama valley? I wasn't sure if "Okutama valley" was referring to the river itself or the area the cafe is in.

He explained to ussaid that they shuttle between Tokyo and Budapest.

I think "said" sounds a little more natural here, but what you had was grammatically correct. I'd reserve "explain" when someone is describing the reason behind something or trying to make something more understandable.

He explained told us that with the help of various people, he built an octagonal building.

"said" would work well here too. Is the octagonal building the same building as the cafe?

Among them, one person, a student from Budapest, stayed at a share-house near the cafe and helped with the construction.

The garden is still under development, but there are several art pieces that presentedmade by a craftsman, and inside the cafe, paintings adorning the walls that were made by his female acquaintance, who areis a top-notch painters, adorned the walls.

Did you mean to say that both the craftsman and his acquaintence were top-notch painters?

There is another large painting still in progress, but it seems sthe painter will come from Osaka to stay for a week in May to complete the painting.

I went with mMORE POLITELY: My wife toand I visited a cafe opened by an acquaintance who lives in Hungary.

NOTE: In polite English, the word "I" is often placed *after* other people to avoid seeming too egocentric.

The located is at the beginningnear the source of thea river the Okutama valley (in western Tokyo) and the natural scenery there is fantastic.

NOTE: Some people outside of Japan might not know *where* Okutama is.

He explained to us that with the help of various people, he built an octagonal buildingMoreover, he mentioned that octagonal building in that valley thanks to the help of many people.

NOTE: Instead of repeating the phrase "He explained" I reworded the sentence.

Among them, one person, a student from Budapest, stayed in a share-house near the cafe and helped with the construction.

The garden is still under development, but there are several art pieces that presenadorning its walls created by a craftsman, and inside the cafe, there are paintings by his female acquaintance, who. Both of them are top-notch painters, adorned the walls.

There is another large painting still in progress, but it seems sheand his lady friend will come from Osaka to stay for a week in May to complete the painting.

A New Cafe

This is 100% correct. I personally write "café," but either way is fine :)

I went with my wife to visitMy wife and I went to a cafeé opewned by an acquaintance who lives in Hungary.

I rarely say "I went with a friend to XYZ"... I almost always say "My friend and I went to XYZ."

I think if someone asked who I went with, I would say "I went with a friend." But usually, I say "My friend and I went..."

TheIt is located is at the beginning ofwhere the river of Okutama vValley begins, and the natural scenery is fantastic.

He explained to us that they (?) shuttles (?) between Tokyo and Budapest.

Who is "they"?

He explainedalso told us that with the help of variousother people, he built an octagonal building.

When I read "various people," I think some are tall, some are short, some are fat, some are thin...

Among them, one person, a student from Budapest, stayed in a share- house near the cafeé and helped with the construction.

The garden is still under developmentconstruction, but there are several art pieces that presencreated by a craftsman displayed there, and inside the cafe, paintings by his female acquaintance, who areis a top-notch painters, adorneds the walls.

What do you mean by "craftsman"?
Also, it's not very common to specify between "male" and "female" acquaintance, unless it's important. Otherwise, it might sound a little negative, like you are surprised that a woman can be a top-notch painter.

There is another large painting that is still in progress, but it seems sthe artist will come from Osaka to stay for a week in May to complete the painting.

The cafe located iswas located at the beginning of the river Okutama valley river and the natural scenery iwas fantastic.

Amongst them, one person, a student from Budapest, stayed at a share-house near the cafe and helped with the construction.

The garden is still under development, but there awere several art pieces that were presented by athe craftsman, and i. Inside the cafe, paintings by his female acquaintance, who are top-notch painters, adorned the walls.

There is another large painting still in progress, but it seems shethe artist will come from Osaka to stay for a week in May to complete the painting.

TheIt's located is at the beginning of the river Okutama valley and the natural scenery is fantastic.

I was a little unsure so I left it. Is the river called Okutama Valley? Or is the river called Okutama and it's located in a valley? Or is the river located somewhere called Okutama valley?

He explained to us that they shuttletravel back and forth between Tokyo and Budapest.

Among them, one person, a student from Budapest, stayed at a share-house near the cafe and helped with the construction.

The garden is still under development, but there are several art pieces that presenconstructed by a craftsman, and inside the cafe, paintings by his female acquaintances, who are top-notch painters, adorned the walls.

You can also start a new sentence instead of using "and" here

There is another large painting still in progress, but it seems that she will come from Osaka toand stay for a week in May to complete the painting.

TheIt is located is at the beginning of the river Okutama valley and the natural scenery is fantastic.

He explained to us that they shuttlmove between Tokyo and Budapest.

Among them, one person, a student from Budapest, stayed at a share-house near the cafe and helped with the construction.

The garden is still under development, but there are several art pieces that presentedwere made by a craftsman, and inside the cafe, paintings by his female acquaintance, who are top-notch painters, adorned the walls.

There is another large painting still in progress, but it seems she will come from Osaka to stay for a week in May to complete ithe painting.