Hi, (:

I'm looking for manga with transport/s to the different world/s
not necessary science fiction
but anything different from the stereotypical magical other world/s themes

Other than that, I'd like any suggestions for really great science fictions
even without the different world/s aspect

and thanks!

Kanata no Astra is exactly what you want.

Must Read Webcomic:
Unsounded

Lists:
Reading
Complete
Western Webcomics

Watashi no Kairos - The Tale of Little Gladiator

[img]https://i.imgur.com/lHjrfaR.jpg[/img]

Milk Closet
Coo's World - fantasy rather than science fiction, but not stereotypical.
The Way of Ryu - assuming the "different" world can be Earth itself.

Kabu no Isaki - See the comments above, also a spoiler of sorts.

A couple of series with parallel worlds:
Inai Boku wa Hotarumachi ni Iru

Babel no Toshokan

A Western webcomic:
Shell

the greatest 'hard' science fiction mangaka is probably HOSHINO Yukinobu and his manga 2001 Ya Monogatari is on par with isaac asimov.

hotel is also great though only the titular chapter is liked by most

i also find TEZUKA Osamu is very good in creating stories from science fiction, drama, historical fictions, etc. some of sci fi stories are in Kuuki no Soko

of course you cannot forget the classic 11-nin Iru!. HAGIO Moto is really masterful in creating psychological drama in science fantasy including manga likeA, A' and Slow Down (HAGIO Moto)

I would like to second recommendation for HOSHINO Yukinobu's works.

And some suggestions from me:

Dosei Mansion

Koukaku Kidoutai (Ghost in the Shell) + its sequels.

Murasakiiro no Qualia + original novel is fully translated too. I highly recommend this one.

Seikai no Monshou (YONEMURA Kouichirou) + original novel is fully translated too. The adaptation is pretty good, but its scanlation is rather slow so it might be better to just read the novel.

Wombs

If you don't mind novels, then also:

Owari no Chronicle (Novel) - it's Science Fantasy rather than pure Sci-fi. This novel features original and well detailed setting, so it is pretty close to what you are looking for.

Shuumatsu Nani Shitemasu ka? Isogashii Desu ka? Sukutte Moratte Ii Desu ka? (Novel) - also a Science Fantasy. Features original and well developed world, just like what you have asked for. Main story is fully translated btw.
There is a manga adaptation too, but it's not that good, as far as I can tell from the only scanlated chapter right now. A lot of the details, particularly world building, are missing in it.