Young used end-terrace house & basement window expansion

Thanks in advance for all the answers.

But it doesn't matter, as a home office, guest room, reading room, the rooms are quite usable.

I see a finished basement. And yes: small windows. For an office or guest room, it should be enough.

Yes, it could become a home office/office.

My considerations regarding the windows are that they not only bring light (which might also be replaceable with electric light), but also fresh air (and of course theoretically can also serve as escape/rescue routes).

Wouldn't the oxygen eventually run out in such a basement room with only one mini window, where the air circulation is probably further limited by the light shaft, if 1 to 2 people stay there for 8 hours, whether sleeping or working (like when everyone in a poorly ventilated classroom eventually almost falls asleep;))?
The windows all logically face the end wall of the house, so cross-ventilation is hardly possible...

I also haven't read anything about a ventilation system in the listing (or did I miss something?), even though the house would probably be modern enough in principle. But maybe it would be easier to retrofit one at least for the basement than windows...

It is probably not approvable as living space with a structural height of 2.25m. Take a look at "42 HBO – Aufenthaltsräume":

(1) 1 Aufenthaltsräume must have a clear room height of at least 2.40 m, in basements and attics at least 2.20 m. 2 In attics, this room height must be present over at least half of their floor area; room parts with a clear height of up to 1.50 m are not considered.
(2) 1 Aufenthaltsräume must be sufficiently ventilated and can be illuminated with daylight. 2 They must have windows with a raw structural dimension of the window openings of at least one eighth of the floor area of the room, including the floor area of glazed extensions and loggias.
(3) Aufenthaltsräume whose use prohibits daylight lighting, as well as sales rooms, bars and restaurants, treatment rooms of the health sector, sports, play, workshop and similar rooms are permissible without windows.
(4) Aufenthaltsräume according to paragraph 3 must be directly connected to escape routes leading outside.

But that does not really prevent you from putting a desk down there as shown in the pictures ;)

It is probably not even approved as living space

But you don’t have to get everything approved. If you set up an office there – why not?
Only in case of (re)sale is it "just" a finished basement, not living space.

Doesn’t the oxygen eventually run out in such a basement room with only a tiny window, where air circulation is probably further restricted by the light well, if 1 to 2 people stay there for 8 hours, whether sleeping or working (like when everyone in a poorly ventilated classroom almost falls asleep;) )

Phew, do you constantly ventilate? There are times when my office is not ventilated for days. If it’s cold outside and the door is open, you don’t notice any limitation, do you? And there is a difference between 24 children consuming air or 1-2 people. I wouldn’t have any problem with that.

Looks tidy, but these high-gloss tiles with the charm of a sterile operating room are not at all my thing.

The basement works well as an office! There's plenty of air coming in.
I would be more interested in whether it gets very hot under the roof in summer.

but these glossy tiles with the charm of a sterile operating room would be nothing for me at all.

I don’t know glossy tiles in the OR, I’m a public health insurance patient ;-)

Very nice terraced house. But the price is already quite steep. I thought it was already expensive here in the southwest. But this is also the Frankfurt catchment area. I think the 1000 euros for an expert are included in the total sum. So if it reassures you, why not. I am doing the same tomorrow, although in my choice of property there is certainly more reason for it. Good luck anyway. The garden looks pretty.