Kaal Sarp Yog is dosha in kundali is a result of one's past karma. It may also happen if the deceased ancestors are displeased or It may occur if a person has harmed a living being/snake either in the present or the previous life as per Hindu mythology and Astrology.
As per astrology when all the planets (Graha) comes between Rahu and Ketu, then signs of Kaal Sarp Yog as regular health problems/Career issues/family issues/delay in work/loss of mental peace is seen in person.
About the location:
Tapovan in Nasik city is the sangam place of two river Kapila and Godavari. As per to Hindu mythologies, Lord Shri Rama, Mata Sita along with brother Laxman had spent the maximum period on this place during 14 years of their Vanvaas in this holy place. The name Tapovan suggests a forest for attaining peace and doing meditation.