I forgot Jantar Mantar! In Jaipur, there is a really really cool astronomical observatory from the 1700s filled with gigantic stone instruments used to make various astronomical measurements. One of the site’s claims to fame is that it has one of the largest sundials in the world (accurate up to 2 seconds!!!).
Here is a picture of the sundial (the crowd is in front of the shadow, which is where you tell the time):
And here is a pic of another measuring instrument. I don’t quite remember what this one is for, I think it has something to do with figuring out which astrological sign we’re in or something. It looks pretty cool, though.