Building a residential/hobby basement underground - What to consider?

Is that roughly understandable?

Yes, thank you! A construction method unknown to me, but described very clearly. Where/how did you seal against moisture?

What is a crazy idea for some is simply an option worth considering for someone else.

The thing with the glass box for training is nice up to the point where it gets warm. I can hardly stand it in the closed garage in midsummer. Therefore, this option would be off the table, even with an appropriate shading system.

But as I said, I am also open to other possibilities to design something like this in order to put my current plan aside.

Attached is a sketch of how I thought it.
Scale 1:200

EDIT: File with 1.6mb too large again :/
I'll have to do it from the PC then, unfortunately

Where/how did you seal against moisture?

Hello Bieber0815 Certainly unconventional. But I saw it as a challenge and wanted to generate as little cost as possible. I only have ground moisture. So I didn’t have to do too much. I laid a full-surface dimpled membrane on the ground. On top of that, 30cm watertight concrete. The walls are treated with thick-bitumen, with 5cm Styrofoam attached, and in front of that towards the fill gravel another dimpled membrane. That should be sufficient. Steven

for the rest
there is actually supposed to be a barbecue area there and then the question arises again how to build it nicely in terms of appearance.

Hello Webmaster-uk

then you should consider building the barbecue area on the cellar. You can make the entrance look good visually. A bit of brainpower, and it works.
You would certainly have to underpin the garage, but that’s not so difficult either. Just labor-intensive.

Steven

I think that's nonsense; no one would build that with a permit, right?

On the contrary, I think a permit does not stop the rumor mill. I consider it possible that the permit will be granted—even if the caseworker shares my assessment as a crazy idea, that is not an obstacle since it is not relevant here. Regarding the efficiency of the solution, I allow myself not to be part of the optimistic faction—more precisely: I suspect strong opposition in the calculation. Nevertheless, it is deserved for whoever enjoys it.