If you inherit such a building and can afford to leave it for the grandchildren... well, then 75k inheritance tax, which was hypothetically assumed here, is probably a small fry?
How do you intend to maintain a property of this size until the solvent grandchildren take over? Heating costs, garden, maintenance?
Of course it will be rented out and hopefully pays for itself until then. What else?
Does anyone now know how the tax office even determines the value?
The tax office determines a current market value, e.g. based on sales in the neighborhood, standard land values, etc. In any case, it is not the value the house had when it was bought 30 years ago, if you had hoped for that. ;)