New single-family house over a bunker from World War II

My partner and I have found a over 1,700 sqm in size with an old bungalow and outbuildings that we like. The price for the size is right, too. During the viewing, it turned out that relatively centrally on the property, under the outbuilding, there is a bunker from the time before World War II. Our plan is to completely renovate or demolish and rebuild the bungalow at a later date to rent it out.

Even plots of land 1700 sqm in size can have small building windows. If I understand correctly, you see the bungalow more as a reserve and primarily want to use a kind of "pipe-head" building plot for your own living at the moment in its "hinterland," i.e., in the second row. It is advisable to at least take a look at the development plan or the cadastral atlas regarding actual building windows in §34 areas. Also, with large plots, parts may be in the outer area; get informed about that.

The bungalow is located at the front of the property by the street. Behind it, probably above the bunker (there are no building plans, no one knows exactly where it begins and ends), we would build a new single-family house to have a nice free view of the trees at the end of the property and privacy. I found nothing on the internet about whether you can simply build a new building over an old bunker. Does anyone here have experience and can give us advice and answer my question?

I only know of a high bunker "within my circle of friends" and can only say that a bunker on a property is a pretty serious legacy issue. Also, the freedoms to just leave it empty may be more limited than little Fritzchen imagines. These things are registered somewhere. At least find out whether the thing lies only under your property. Entrances can be very hidden; there will be at least one ventilation (maybe even in the bungalow’s basement, behind a fake wine rack like in an Edgar Wallace movie, haha), and the risk of becoming known in the lost places scene should not be underestimated. Ask old people in the village, retired local mayors, or so. In summary, I see in such a bonus property less of a creepy Miss Marple thrill and more of a blank check for unforeseen trouble.