The site of Buddha's first sermon, Sarnath is a peaceful place to get away from the havoc of Varanasi and learn more about Buddhism, which was once the dominant religion in India.
More of an area than a specific site, Sarnath is full of Buddhist temples built by devotees from various countries, including Tibet, China, and Thailand.
The Thai temple, with its huge Buddha, is the most interesting, but the others make a worthwhile stop and it's always interesting to see how the representations of Buddha differ from one country to another.
The Archaeological Museum, which costs 5INR, is not only air-conditioned but informative, with good displays and lots of information. The original statues from the now empty Dhamekh Stupa and Ashoka Pillar and the calming music are just what you need after too much time in Varanasi.
The Dhamekh Stupa itself costs 100INR, but it's probably not worth paying for unless you really want to get up close. The parks surrounding it, which offer much of the same views, are free.
An auto-rickshaw from Varanasi should cost around 100INR each way. If the driver stays and drives you around the compound, it'll be a bit more.
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