Google Arts and Culture offers you to take a virtual tour of the 13th century observatory Jantar Mantar in Delhi. At the opening view (see the website link below), the Google tour explains: "Innovations in architectural astronomy: The Jantar Mantar Obervatory, Delhi's outdoor astronomical observatory is the earliest of five observatories built by Sawai Jai Singh II across India. It is dominated by a huge sundial and houses other innovative instruments that help plot the course of heavenly bodies...."

"The Maharaja designed four similar observatories in Jaipur, Ujjain, Mathura and Varanasi to help and improve upon the studies of space and time. The Jantar Mantar in Jaipur is now the largest among them." Google gives us a glipse of the large equatorial dial of the Man Singh Observatory in Varanasi and then focuses on the four large brick and plaster instruments at Jantar Mantar: the Ram yantra, two circular structures next to each other used to observe celestial objects; the Samrat yantra, one of the largest equatorial dials in the world with stairs leading to the top of the triangular gnomon (looking like stairs to the heavens) and surrounded by a large equatorial band to measure solar time; the Jai Prakash yantra that consist of two elaborate sunken hemispheres so large that there are stairs from the bottom leading between huge longitudinal bands; and the Misra yantra, which is shaped like a heart and is composed of five different sun and alignment instruments to determine the shortest and longest days of the year at the solstices.

Take a personal visit to these historic astronomical and solar instruments at: The Jantar Mantar Observatory - Google Arts & Culture