Observatories pl. : of Observatory

Example:
Which of the following is not a good reason to place Observatories on remote mountain tops?

Taxonomy
observatory, radio observatories, the Earth's atmosphere, space telescopes, astronomical observatories, telescope, Ground-based observatories, Space-based observatories, free encyclopedia, The Hubble Space Telescope, Islamic History, Astronomy Today, Volcano observatories, instrument, EMI, Muslims, Chaisson, McMillan.

Defination from the web:
observatories are located far from major centers of population, to avoid the effects of light pollution. ... The ideal locations for modern observatories are sites that have dark skies, a large percentage of clear nights per year, dry air, ...