Ground floor bungalow approx. 115m² for 2 persons

If a lack of motivation for sports sets in here, we have a room for which we currently have no use.

And so you have the area of a room, which is then pure hallway space and amounts to about 12 sqm and can't even be used as a real room (caregiver in old age) or something like that.

Treadmill etc. are compactly storable.

Where will those be stored then? And doesn't it increase the lack of motivation if you always have to set everything up first?

Treadmills etc. are compact and can be stored away. We only need space when using them. We have abandoned the idea of having our own gym. If a lack of motivation for sports sets in, we have a room for which we currently have no use.

The cake tester Erwin Grosche recommends, in the series "Cakes in Unusual Places" transferred to your construction project, to put the treadmill in the gaming room. Sports equipment "out of sight, out of mind" is for the same people who sign up at the gym on January 2nd and then fatten both the operator with unused membership fees and themselves on the sofa. A "gym room" as a New Year's resolution room is money thrown away. Better to do lead pouring and Dinner for One, and go for a walk during the Chancellor's New Year's speech.

Well, a cleverly planned room currently designated as a "sports room" doesn’t hurt as a couple either. You never know how life will develop; as mentioned, maybe a caregiver or separate sleeping areas due to a corresponding illness, etc.

And if this extra room is well planned in terms of location, it can also become a sauna room with a bathroom connection, etc. ... Especially since a second bathroom with a shower is now also planned.

And generally the property, which might be easier to sell in old age (perhaps moving to a nursing home).

Well, a cleverly planned room currently designated as a "gym room" doesn't hurt as a couple either. You never know how life will develop, [...] And generally the [...] better marketable property.

Yes, basically "couple" should not mean "zero-child-room property," simply because that reduces marketability on resale. You don't even have to become frail; a job change two federal states away is a compelling argument for moving house (and fortunately much more common than suddenly needing a wheelchair).

I also belong to the group: 2 bedrooms - that can be used in many ways, children's room, office, separate sleeping (permanently or due to illness), gaming room, sports room, hobby room (e.g. sewing, crafting, painting, tinkering) or you have a parent staying with you for a few weeks, for some reason.