The Mathematical Tower of Kremsmünster abbey (observatory Specula cremifanensis), seen from Gymnasial arcades, belongs to the most significant historical observatories in the world and is registered under International Astronomical Union (IAU) code 539. The IAU declared it as Outstanding Astronomical Heritage.
<a href="//commons.wikimedia.org/wiki/User:Isiwal" title="User:Isiwal">Isiwal</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>