Observatorio Astronomico Nacional, Sierra de San Pedro Martir

The Observatorio Astronomico Nacional sits at roughly 2,800 metres on a pine-forested ridge inside San Pedro Martir National Park, in the Sierra de San Pedro Martir of Ensenada Municipality, Baja California, Mexico. Operated by Mexico's national university, UNAM, the site houses several research telescopes, including instruments up to 2.1 metres in aperture, chosen for this location because the combination of altitude, dry air and distance from major light sources gives it some of the clearest, most stable night skies in the northern hemisphere -- comparable to sites in Hawaii and Chile used for similar reasons. The park itself is a high-altitude pine and fir forest, a striking contrast to the desert lowlands most visitors associate with Baja California, with granite peaks, seasonal streams and, in winter, snow.

Daytime visitors can drive the access road to the park and reach a viewpoint near the observatory domes, though the domes themselves are not open for interior tours without prior arrangement through UNAM, since the site remains an active research facility rather than a public visitor centre. The real draw for most visitors is not the daytime dome view but the night sky itself: camping in the park after dark, away from the light pollution of the coast, reveals a Milky Way and star field rarely visible anywhere else in the region.

A full visit requires a full day from the coast given the 100 km of paved mountain road climbing from Highway 1 at San Telmo or Colonet, and most visitors either camp overnight in the park or plan to descend before dark. May through October is the most reliable season, both for clear weather and for road access, since the route can close after winter snow; timing a visit around the new moon maximises how dark and star-filled the sky appears. There is no fuel or services within the park, so vehicles should be filled in Colonet before the climb.