Since Galileo invented the first telescope in 1609, humanity made huge progress in the exploration of the universe. And today, it would be unforgivable not to take advantage of the modern technologies and visit some of the world’s best observatories at least once. Luckily, there are many options to choose from.

Roque de los Muchachos Observatory in Spain is home to the world’s biggest telescope called the Gran Telescopio Canarias. Measuring 409 inches across, the telescope sits on the volcanic peak, 7,438 feet above the ground. The private tours last 70-90 minutes and must be booked in advanced online.

Alma Observatory in Chile is a result of collaboration among North America, Europe, South Asia and Chile and consists of 66 giant telescopes, which together help to compose very high-resolution images of the universe. Suited 16,404 feet above sea level, the observatory has perfect conditions for watching the night sky including its high altitude, dry climate and lack of clouds. It’s open to the public every Saturday and Sunday morning. To be admitted, visitors must register online in advance.

Hawaii’s Mauna Kea Observatories is the place to go in the U.S. According to the University of Hawaii, the combined power of all telescopes in the observatory is “sixty times greater than that of the Hubble Space Telescope.” The observatory offers stargazing programs on Tuesday, Wednesday, Friday and Saturday evenings from 7 p.m. to 10 p.m.

And the South African Astronomical Observatory is the largest in the Southern Hemisphere. It’s known for its giant telescope SALT (Southern African Large Telescope) and is responsible for the discovery of the hourglass nebula, one of the most famous nebulae caught by the Hubble Space Telescope. The facilities are open to visitors on Monday to Saturday from 10:30 a.m. to 2:30 p.m. There are also night tours offered at different times on Monday, Wednesday, Friday and Saturday.

Roque de los Muchachos Observatory, Photo Credit: Bob Tubbs