Where is the best place to advertise a piece of land (outdoor area)?

we could follow up again with the municipality itself to see if there are any plans for reclassification...

That would bring little: the municipality will tell you very little (or nothing) about anything that will not be visible at the latest in the second coming budget year – these investigations must be done by yourself: what is the population development, will the state development plan see / upgrade / downgrade the municipality in its current position in the long term, at what pace will new building land designations come closer, etc. A few years ago there were (now expired) facilitations for development plan procedures, which were partly used / partly not or only rudimentarily. Currently, infill developments are more in demand than new plans; commercial, conversion, and other brownfields will certainly be (re)activated before reserves in the outer areas; great hopes are placed in gap cadasters ...

We don’t live in Germany, that would be a somewhat long trip :) My brother lives somewhat nearby...

Then the brother will have to listen carefully, offshore you are too far out of range there.

As I read it, I would definitely sell the property. I have done this several times in the past and in both directions, always with the basic approach "I buy what I like or find enjoyable for some reason" and "I sell what doesn't interest me." Holding onto a property just because you happened to inherit it? Anyone who argues "it might someday" would have to buy properties somewhere at any time because "it might." By the way, €8/sqm is quite a lot for flood-prone pastureland. I have never paid that much even for good pastureland.

We're talking here about 37.6k divided by two - you're not serious that they now decide hop or top...

even if you might not be able to imagine that ;) sometimes it's just hundreds of available euros that can have a decisive impact on life-changing things. At least in my personal memory range, such moments are still relatively clearly recognizable. Presumably, the OP who lives abroad experiences it the same way, otherwise he wouldn't say so.
Moreover, the lease must be taxed, the sales proceeds probably not (although I am not a tax expert).

By the way, €8/sqm for flood-prone pastureland is quite a lot. I've never paid that much even for good pastureland.

Here in the flat Münsterland, €10 is currently being asked for arable land.

@11ant even if you might not be able to imagine it ;) sometimes it is only hundreds of available euros that can have a decisive influence on life-changing things. At least within my personal memory range, such moments are still relatively clearly recognizable.

Not only in yours. See also post #11.

Thank you very much for all the answers, these are very helpful assessments / opinions.

Well, just to put it into perspective, we are not poor or anything. But also not so wealthy that it wouldn’t matter to us to get €15,000+ just like that :)