House too big, what to do with the extra rooms?

Well, why does it have to be a house then, if the probability of finding something suitable is practically zero? Why not just an [ETW]. The question is rhetorical, I really don't need an answer to that now (in the style of 20 passive-aggressive counter-questions), I think you @ TE can quietly answer that yourself.

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So because I was once small too, should I now set up a playroom??

No, you should just question your harsh statement "I hate children." When I hate someone, people generally assume I wish nothing good for that person. You had already responded here not exactly kindly with the term "nonsense." Both expressions cast a bad light on how you interact with other people who, for the most part, only wanted to help you here selflessly. A friendlier tone is not too much to ask. Unfortunately, this is often lacking on the internet. The tone makes the music here as well.

You had mentioned a hobby workshop and I thought that it might possibly be related to your artistic activity. That’s where my idea came from. It has now turned out to be mistaken, however, you also haven’t given many details about your hobbies, profession, etc., so that one could really come up with individual ideas. I could now also suggest a whirlpool, sauna, ball pit, music room, ... but that wouldn’t really help you either.
85m² is really quite small for a house, so the options are limited. However, there is quite a bit of leeway between 85 and 170m². Around 110m², at least in our area, you can find quite a few. Moreover, these houses are often not so expensive, as they are too small for most (families) and thus there aren’t so many interested buyers.

Tonight he is round as a ball, that's how much he is being fed ;)

The hobby workshop is supposed to be on the ground floor anyway. I don’t need two workshops. In the area of 110sqm, I do find houses, but the problem is again that many of these houses are divided into two levels and mostly have a steep spiral staircase. I can’t manage something like that. In general, the ground floor area should be quite large. That’s more like a bungalow. Most bungalows, however, are found rather in new development areas or more expensive residential neighborhoods. I don’t want to go there either.

Football room, there is nothing cooler than playing football at home :D, you just need a small ball and 2 mini goals