The Hardtberg Tower was closed just a week after it opened.
The reason is loose steps, as the city of Königstein announced on Monday.
The Hochtaunus police department investigates and does not rule out vandalism, as a spokesman for the West Hesse police headquarters says.
The officials were informed by the city on Friday that the tower could no longer be entered safely and they secured evidence.
Florentine Fritzen
Correspondent in the Hochtaunus district
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According to the city, at several points on the stairs to the 32-meter-high steel observation tower, bolts that are not only held in place by nuts but are also glued are loose.
"I don't want to anticipate the ongoing investigations, but it is very likely that several stages were deliberately handled here," said Mayor Leonhard Helm (CDU).
Together with the architect, it is checked whether screws could have become loose for another reason.
The tower was opened last Saturday.
The mayor calls it "sad and sobering" when people with "high criminal energy potential" destroy beautiful things.
If there is another cause, it will be fixed as soon as possible.
The tower will remain closed during the investigation.