The Observatorio Astronómico Nacional, tucked behind the Casa de Nariño on Calle 11, is the oldest scientific institution in Colombia and one of the oldest astronomical observatories in the Americas. It was built by botanist Francisco José de Caldas under the direction of José Celestino Mutis and opened in 1803.
The tower and observatory dome still stand intact in a small garden. It is not a working observatory — the light pollution makes that impossible — but the building is a remarkable survival from the late colonial period. Guided visits are available through the Universidad Nacional, which administers the site. Coordination required in advance; check the Universidad Nacional's website for current visit arrangements.